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A TEXT-BOOK 

OF 

PRECIOUS STONES 

FOR JEWELERS 

and 

^THE GEM-LOVING PUBLIC 



BY 

FRANK B. WADE, B.S. 

'I 

HEAD OF THE DEPARTMENT OF CHEMISTRY, SHORTRIDGE HIGH 

SCHOOL, INDIANAPOLIS, IND. 

AUTHOR OF "DIAMONDS: A STUDY OF THE FACTORS THAT 

GOVERN THEIR VALUE" 



ILLUSTRATED 



G. P. PUTNAM'S SONS 

NEW YORK AND LONDON 

Ube Tknicftetbocfeer press 

1918 






Copyright, 1918 

BY 

FRANK B. WADE 



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MAR -S 1918 



Ube IknicherbocFtet f)cess, View IBocit 



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481990 



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PREFACE 



IN this little text-book the author has tried 
to combine the trade information which 
he has gained in his avocation, the study of 
jH"ecious stones, with the scientific knowledge 
bearing thereon, which his vocation, the teaching 
of chemistry, has compelled him to master. J ^ 
In planning and in writing the book, every 
effort has been made to teach the fundamental 
principles and methods in use for identifying 
precious stones, in as natural an order as pos- 
sible. This has been done in the belief that the 
necessary information will thus be much more 
readily acquired by the busy gem merchant 
or jeweler than would nave been the case had 
the material been arranged in the usual sys- 
tematic order. The latter is of advantage 
for quick reference after the fundamentals of 
the subject have been mastered. It is hoped, 
however, that the method of presentation used 



IV 



Preface 



in this book will make easy the acquisition of 
a knowledge of gemology and that many who 
have been deterred from studying the subject 
by a feeling that the difficulties due to their lack 
of scientific training were insurmountable, will 
find that they can learn all the science that is 
really necessary, as they proceed. To that end 
the discussions have been given in as untech- 
nical language as possible and homely illustrat- 
ions have in many cases been provided. 

Nearly every portion of the subject that a 
gem merchant needs to know has been con- 
sidered and there is provided for the interested 
public much material which will enable them 
to be more intelligent purchasers of gem-set 
jewelry, as well as more appreciative lovers of 
Nature's wonderful mineral masterpieces. 

F. B. W. 



Indianapolis, 

December 26, IQ16 



INTRODUCTION 

OECAUSE of the rapid increase in knowl- 
edge about precious stones on the part 
of the buying public, it has become necessary 
for the gem merchant and his clerks and sales- 
men to know at least as much about the subject 
of gemology as their better informed customers 
are likely to know. 

In many recent articles in trade papers, 
attention has been called to this need, and to 
the provision which Columbia University has 
made for a course in the study of gems. The 
action of the National Association of Gold- 
smiths of Great Britain in providing annual 
examinations in gemology, and in granting 
certificates and diplomas to those who success- 
fully pass the examinations, has also been re- 
ported, and it has been suggested that some such 



vi Introduction 

/ 
course should be pursued by jewelers' associa- 
tions in this country. The greatest difficulty 
in the way of such formal study among our 
jewelers and gem merchants is the lack of time 
for attendance on formal courses, which must 
necessarily be given at definite times and in 
definite places. 

As a diamond salesman was heard to say 
recently: "The boss said he wanted me to take 
in that course at Columbia, but he didn't tell 
me how I was going to do it. Here I am a 
thousand miles from Columbia, and it was only 
six weeks ago that he was telhng me I ought 
to take that coiirse. I can't stay around New 
York all the time." Similarly those whose 
work keeps them in New York might object 
that their hours of employment prevented 
attendance on day courses, and that distance 
from the university and fatigue prevent 
attendance on night courses. The great mass 
of gem dealers in other cities must also be 
considered. 



Introduction vii 

It will therefore be the endeavor of this book 
to provide guidance for those who really want 
to make themselves more efficient in the gem 
business, but who have felt that they needed 
something in the way of suggestion regarding 
what to attempt, and how to go about it. 

Study of the sort that will be suggested 
can be pursued in spare moments, on street 
cars or elevated trains, in waiting rooms, or 
in one's room at night. It will astonish many 
to find how much can be accomplished by 
consistently utilizing spare moments. Booker 
T. Washington is said to have written in such 
spare time practically all that he has published. 

For the practical study of the gems them- 
selves, which is an absolutely essential part of 
the work, those actually engaged in the trade 
have better opportunities than any school 
could give and, except during rush seasons, there 
is plenty of time during business hours for such 
study. No intelligent employer will begrudge 
such use of time for which he is paying, if the 



viii Introduction 

thing be done in reason and with a serious view 
to improvement. The frequent application 
of what is acquired, as opportunity offers, in 
connection with ordinary salesmanship, will help 
fix the subject and at the same time increase 
sales. 

Many gem dealers have been deterred from 
beginning a study of gems because of the seem- 
ing difficulties in connection with the scientific 
determination of the different varieties of stones. 
Now science is nothing but boiled-down com- 
mon sense, and a bold front will soon convince 
one that most of the difficulties are more ap- 
parent than real. Such minor difficulties as 
exist will be approached in such a manner 
that a little effort will overcome them. For 
those who are willing to do more work, this 
book will suggest definite portions of particular 
books, which are easily available, for reference 
reading and study — but the lessons themselves 
will attempt to teach the essential things in as ' 
simple a manner as is possible. 



Introduction 



IX 



Perhaps the first essential for the gem mer- 
chant is to be able surely to distinguish the 
various stones from one another and from 
synthetic and imitation stones. 

That such ability is much needed will be 
clear to anyone who in casting a backward 
glance over his experience recalls the many 
serious mistakes that have come to his knowl- 
edge. Many more have doubtless occurred 
without detection. Several times recently the 
author has come across cases where large 
dealers have been mistaken in their determina- 
tion of colored stones, particularly emeralds. 
Only the other day a ring was brought to me 
that had been bought for a genuine emerald 
ring after the buyer had taken it to one of the 
dealers in his city and had paid for an examina- 
tion of it, which had resulted in its being de- 
clared genuine. On examining the stone with 
a lens of only moderate power, several round 
air bubbles were noted in it, and on barely 
touching it with a file it was easily scratched. 



X Introduction 

The material was green glass. Now, what was 
said about the dealer who sold it and the one 
who appraised it may be imagined. The long 
chain of adverse influence which will be put 
in action against those dealers, even though 
the one who sold the stone makes good the loss, 
is something that can be ill afforded by any 
dealer, and all this might have been avoided 
by even a rudimentary knowledge of the means 
of distinguishing precious stones. The dealer 
was doubtless honest, but, through careless- 
ness or ignorance, was himself deceived. 

Our first few lessons will therefore be con- 
cerned chiefly with learning the best means of 
telling the different stones from one another. 



CONTENTS 



Preface . 

LESSON 
I- 

II.- 
III.- 

IV.T- 

V.- 
VI.- 



-How Stones are Distinguished 
FROM One Another 

-Refraction 

-Double Refraction 

-Absorption and Dichroism 

-Specific Gravity 

-Specific Gravity Determina- 
tions .... 



VII. — Luster and Other Reflection 
EffectsI 

VIII. — Hardness 

IX. — Hardness (Continued) 
X. — Dispersion 

XI. — Color 

XII. — Color (Continued) 
XIII. — Color (Continued) 
XIV. — Color (Concluded) 



PAGE 

iii 



I 

5 

8 

15 
23 

31 

38 
47 

55 
60 
66 

75 
87 
93 



Xll 





Contents 




Lesson 




PAGE 


XV.- 


—How TO Tell Scientific Stones 






FROM Natural Gems 


99 


XVI.- 


—How TO Test an "Unknown" 






Gem ..... 


109 



XVII. — Suitability of Stones for 
Various Types of Jewels, as 
Determined by Hardness, 
Brittleness, and Cleava- 
bility . . . . -119 

XVIII. — Mineral Species to which the 
Various Gems Belong and 
THE Chemical Composition 

THEREOF . . . .133 

XIX. — The Naming of Precious 

Stones .... 149 

XX. — The Naming of Precious 

Stones {Concluded) . . 164 

XXI. — Where Precious Stones are 

Found ..... 179 

XXII. — How Rough Precious Stones 

are Cut .... 201 

XXIII. — How Rough Precious Stones 
are Cut, and What Con- 
stitutes Good "Make" 
{Concluded) . . , .213 



Contents xiii 

LESSON PAGE 

XXIV. — Forms Given to Precious 

Stones . . . .227 

XXV. — Imitations of Precious Stones 237 

XXVI. — Alteration of the Color of 

Precious Stones . . . 250 

XXVII.— Pearls 258 

XXVIII. — Cultured Pearls and Imita- 
tions OF Pearls . . -277 

XXIX. — The Use of Balances, and the 
Unit of Weight in Use for 
Precious Stones . . . 283 

XXX. — Tariff Laws on Precious and 

Imitation Stones . .294 

Bibliography . . . .301 

Index . . , , . 305 



A Text Book of Precious 
Stones 



LESSON I 



HOW STONES ARE DISTINGUISHED FROM ONE 
ANOTHER 

Precious Stones Distinguished by their Pro^ 
perties. One precious stone is best distin- 
guished from another just as substances of 
other types are distinguished, that is to say, 
by their properties. For example, salt and 
sugar are both white, both are soluble in water, 
and both are odorless. So far the italicized 
properties would not serve to distinguish the 
two substances. But sugar is sweet while salt 
is salty in taste. Here we have a distinguishing 



2 Precious Stones 

property. Now, just as salt and sugar have 
properties, so have all precious stones, and while, 
as was the case with salt and sugar, many- 
precious stones have properties in common, yet 
each has also some properties which are distinc- 
tive, and which can be relied upon as differen- 
tiating the particular stone from other stones. 
In selecting properties for use in distinguishing 
precious stones, such properties as can be de- 
termined by quantity, and set down in numbers, 
are probably more trustworthy than those 
that can be observed by mere inspection. 
Those also which have to do with the be- 
havior of light in passing through the stone are 
extremely valuable. 

Importance of Numerical Properties. It is 
because gem dealers so often rely upon the more 
obvious sort of property, such as color, that 
they so frequently make mistakes. There 
may be several different types of stones of a 
given color, but each will be found to have 
its own numerical properties such as density, 



How Stones are Distinguished 3 

hardness, refractive power, dispersive power, 
etc., and it is only by an accurate determina- 
tion of two or three of these that one can be 
sure what stone he has in hand. It must next 
be our task to find exactly what is meant by 
each of these numerical properties, and how one 
nl9,y determine each with ease and exactness. 



LESSON II 

REFRACTION 

Explanation of Refraction. Perhaps the 
surest single method of distinguishing precious 
stones is to find out the refractive index of the 
material. To one not acquainted with the 
science of physics this calls for some explana- 
tion. The term refraction is used to describe 
the bending which light undergoes when it 

A 




Refraction 5 

passes (at any angle but a right angle) from 
one transparent medium to another. For 
example, when light passes from air into water, 
its path is bent at the surface of the water and 
it takes a new direction within the water. (See 

Fig. I.) 

•A B represents the path of light in the air 
and B C its path in the water. 

While every gem stone refracts light which 
enters it from the air, each stone has its own 
definite ability to do this, and each differs from 
every other in the amount of bending which it can 
bring about under given conditions. The accu- 
rate determination of the amount of bending 
in a given case requires very finely constructed 
optical instruments and also a knowledge of 
how to apply a certain amount of mathematics. 
However, all this part of the work has already 
been done by competent scientists, and tables 
have been prepared by them, in which the 
values for each material are put down. 

The Herbert-Smith Refractometer. There is 



6 Precious Stones 

on the market an instrument called the Herbert- 
Smith refractometer, by means of which any- 
one with a little practice can read at once on the 
scale within the instrument the refractive index, 
as it is called, of any precious stone that is not 
too highly refractive. (Its upper limit is 1. 80. 
This would exclude very few stones of im- 
portance, i. e., zircon, diamond, sphene, and 
demantoid garnet.) 

Those readers who wish to make a more 
intensive study of the construction and use of 
the refractometer will find a very full and 
complete account of the subject in Gem-Stones 
and their Distinctive Characters, by G. F. 
Herbert-Smith, New York; James Pott & Co., 
1912. Chapter IV., pp. 21-36. The Herbert- 
Smith refractometer is there described fully, 
its principle is explained and directions for 
using it are given. The price of the refracto- 
meter is necessarily so high (duty included) 
that its purchase might not be justified in the 
case of the smaller retailer. Every large dealer 



Refraction 7 

in colored stones, whether importer, whole- 
saler, or retailer, should have one, as by its use 
very rapid and very accurate determinations of 
stones may be made, and its use is not confined 
to unmounted stones, for any stone whose 
table facet can be applied to the surface of the 
lens in the instrument can be determined. 



LESSON III 

DOUBLE REFRACTION 

Explanation of Double Refraction. In Les- 
son 11. we learned what is meant by refraction 
of light. While glass and a small number of 
precious stones (diamond, garnet, and spinel) 
bend light as was illustrated in Fig. i, practi- 
cally all the other stones cause a beam of light 
on entering them to separate, and the path of 
the light in the stone becomes double, as shown 
in Fig. 2. 

This behavior is called double refraction. It 
may be used to distinguish those stones which 
are doubly refracting from those which are not. 
For example, in the case of a stone which is 
doubly refracting to a strong degree, such as 
a peridot (the lighter yellowish green chrysolite 
is the same material and behaves similarly 



Double Refraction 9 

toward light), the separation of the light is so 
marked that the edges of the rear facets, as 
seen through the table, appear double when 
viewed through a lens. A zircon will also 
similarly separate light and its rear facets also 
appear double lined as seen with a lens from 
the table of the stone. The rarer stones, 




FIG. 2. 

sphene and epidote, likewise exhibit this prop- 
erty markedly. Some colorless zircons, when 
well cut, so closely, resemble diamonds that 
even an expert might be deceived, if caught off 
his guard, but this simple test of looking for 



10 Precious Stones 

the doubled lines at the back of the stone would 
alone serve to distinguish the two stones. 

A Simple but very Valuable Test for the 
Kind of Refraction of a Cut Stone. In the 

case of most of the other doubly refracting 
stones the degree of separation is much less 
than in peridot and zircon, and it takes a well- 
trained and careful eye to detect the doubling 
of the lines. Here a very simple device will 
serve to assist the eye in determining whether 
a cut stone is singly or doubly refracting. 
Expose the stone to direct simlight and hold 
an opaque white card a few inches from the 
stone, in the direction of the sun, so as to get 
the bright reflections jrom within the stone 
reflected onto the card. 

If the material is singly refractive (as in the 
case of diamond, garnet, spinel, and glass), 
single images of each of the reflecting facets 
will appear on the card, but if doubly refract- 
ing — even if slightly so — double images will 
appear. When the stone is slightly moved, 



Double Refraction ii 

these pairs of reflections will travel together as 
pairs and not tend to separate. The space 
between the two members of each pair of re- 
flections serves to give a rough idea of the degree 
of the double refraction of the material if com- 
pared with the space between members in the 
case of some other kind of stone held at the 
same distance from the card. Thus zircon 
separates the reflections widely. Aquamarine, 
which is feebly doubly refracting, separates 
them but slightly. 

It will be seen at once that we have here a 
very easily applied test and one that requires 
no costly apparatus. It is, furthermore, a 
sure test, after a little practice. For example, 
if one has something that looks like a fine 
emerald, but that may be glass, all one need to 
do is to expose it in the sun, as above indicated. 
If real emerald, double images will be had (very 
close together, because emerald is but feebly 
doubly refracting). If glass, the images on 
the card will be single. 



12 Precious Stones 

Similarly, ruby can at once be distinguished 
from even the finest garnet or ruby spinel, as 
the last two are singly refracting. So, too, are 
glass imitations of ruby and ruby doublets 
(which consist of glass and garnet). This test 
cannot injure the stone, it may be applied to 
moimted stones, and it is reliable. For stones 
of very deep color this test may fail for lack 
of sufficiently brilliant reflections. In such a 
case hold the card beyond the stone and let 
the sunlight shine through the stone onto the 
card, observing whether the spots of light are 
single or double. 

The table below gives the necessary informa- 
tion as to which stones show double and which 
single refraction. 

Table Giving Character of Refraction in the Principal 
Gems 

Refraction Single: 
Diamond 

Garnet (all types) • 

Spinel 
Opal 
Glass 



Double Refraction 13 

Difference between 
highest and lowest 
refractive indices 
Refraction Double 

Sphene 084 

Zircon 053 

Benitoite 047 

Peridot or chrysoKte 038 

Epidote 031 

Tourmaline 020 

•Kunzite 015 

Ruby and sapphire 009 

Topaz (precious) 009 

Amethyst and quartz topaz 009 

Emerald and aquamarine 007 

Chrysoberyl 007 

The student should now put into practice 
the methods suggested in this lesson. Look 
first for the visible doubling of the lines of the 
back facets in peridot (or chrysolite) ; then in 
zircon; then in some of the less strongly doubly 
refracting stones; then try the sunlight-card 
method with genuine stones and with doublets 
and imitations until you can tell every time 
whether you are dealing with singly or doubly 
refracting material. When a stone of unknown 
indentity comes along, try the method on it 
and thus assign it as a first step to one or the 



14 Precious Stones 

other class. Other tests will then be necessary 
to definitely place it. 

Differences in Refraction Due to Crystal 
Form. The difference in behavior toward light 
of the singly and doubly refracting minerals de- 
pends upon the crystal structure of the mineral. 
All gems whose crystals belong in the cubic sys- 
tem are singly refracting in all directions: In 
the case of some other systems of crystals the ma- 
terial may be singly refracting in one or in two 
directions, but doubly refracting in other direc- 
tions. No attention need be paid to these 
complications, however, when using the sunlight- 
card method with a cut stone, for in such a case 
the light in its course within the stone will have 
crossed the material in two or more directions, and 
the separation and consequent doubling of image 
will be sure to result. For those who wish to 
study double refraction more in detail, Chapter 
VI., pages 40-52, of G. F. Herbert-Smith's Gem- 
Stones will serve admirably as a text. As an alter- 
native any text -book on physics will answer. 



LESSON IV 

ABSORPTION AND DICHROISM 

Cause of Color in Minerals. In Lesson III. 

we saw that many gem materials cause light 

that enters them to divide and take two paths 

within the material. Now all transparent 

materials absorb light more or less; that is, 

they stop part of it, perhaps converting it into 

heat, and less light emerges than entered the 

stone. If light of all the rainbow colors (red, 

orange, yellow, green, blue, violet) is equally 

absorbed, so that there is the same relative 

amount of each in the light that comes out as 

in the light that went into a stone, we say that 

the stone is a white stone; that is, it is not a 

colored stone. If, however, only blue light 

succeeds in getting through, the rest of the 

15 



1 6 Precious Stones 

white light that entered being absorbed within, 
we say that we have a blue stone. 

Similarly, the color of any transparent 
material depends upon its relative degree of 
absorption of each of the colors in white light. 
That color which emerges most successfully 
gives its name to the color of the stone. Thus 
a ruby is red because red Hght succeeds in 
passing through the material much better than 
light of any other color. 

Unequal Absorption Causes Dichroism. All 
that has been said so far applies equally well to 
both singly and doubly refracting materials, but 
in the latter sort it is frequently the case, 
in those directions in which light always divides, 
that the absorption is not equal in the two beams 
of light (one is called the ordinary ray and the 
other the extraordinary ray). 

For example, in the case of a crystal of ruby, 
if white light starts to cross the crystal, it not 
only divides into an ordinary ray and an extra- 
ordinary ray, but the absorption is different in 



Absorption and Dichroism 17 

the two cases, and the two rays emerge of 
different shades of red. With most rubies one 
ray emerges purplish-red, the other yellowish- 
red. 

It will at once be seen that if the human eye 
could distinguish between the two rays, we 
woilld have here a splendid method of deter- 
mining many precious stones. Unfortunately, 
the eye does not analyze light, but rather 
blends the effect so that the unaided eye gives 
but a poor means of telling whether or not a 
stone exhibits twin colors, or dichroism, as it 
is called. (The term signifies two colors.) 
A well-trained eye can, however, by viewing 
a stone in several different positions, note the 
difference in shade of color caused by the 
differential absorption. 

The Dichroscope. Now, thanks to the scien- 
tific workers, there has been devised a rela- 
tively simple and comparatively inexpensive 
instrument called the dichroscope, which enables 
one to tell almost at a glance whether a stone is 



i8 



Precious Stones 



or is not dichroic. The construction is indicated 
in the accompanying drawing and description. 




The Dichroscope 
If the observer looks through the lens (A) 



A 






yA 






0© 



Fig. 3. 

A, simple lens; B, piece of Iceland spar with 

glass prisms on ends to square them 

up; C, square hole. 



Fig. 4. 



toward a bright light, as, for example, the sky, 
he apparently sees two square holes, Fig. 4. 



Absorption and Dichroism 19 

What has happened is that the light passing 
through the square hole (C of Fig. 3) has 
divided in passing through the strongly doubly 
refracting Iceland spar (B of Fig. 3) and two 
images of the square hole are thus produced. 

If now a stone that exhibits dichroism is held 
in front of the square hole and viewed toward 
the light, two images of the stone are seen, 
one due to its ordinary ray (which, as was said 
above, will have one color), and the other due 
to its extraordinary ray (which will have a 
different color or shade of color), thus the 
color of the two squares will be different. 

With a singly refracting mineral, or with 
glass, or with a doubly refracting mineral when 
viewed in certain directions of the crystal 
(which do not yield double refraction) the 
colors will be alike in the two squares. Thus 
to determine whether a red stone is or is not a 
ruby (it might be a garnet or glass or a doublet, 
all of which are singly refracting and hence can 
show no dichroism), hold the stone before the 



20 Precious Stones 

hole in the dichroscbpe and note whether or 
not it produces twin colors. If there seems to 
be no difference of shade turn the stone about, 
as it may have accidentally been placed so 
that it was viewed along its direction of single 
refraction. If there is still ho dichroism it is 
not a ruby. (iVo/e.— Scientific rubies exhibit 
dichroism as well as natural ones, so this test 
will not distinguish them.) 

A dichroscope may be had for from seven to 
ten dollars, according to the make, and every- 
one who deals in colored stones shotild own 
and use one. 

Not all stones that are doubly refracting 
exhibit dichroism. White stones of course 
cannot exhibit it even though doubly refract- 
ing, and some colored stones, though strongly 
doubly refracting, do not exhibit any noticeable 
dichroism. The zircon, for example, is strongly 
doubly refracting, but shows hardly any dis- 
chroism. 

The test is most useful for emerald, ruby. 



Absorption and Dichroism 21 

sapphire, tourmaline, kunzite and alexandrite, 
all of which show marked dichroism. 

It is of little use to give here the twin colors 
in each case as the shades differ with different 
specimens, according to their depth and type 
of color. The deeper tinted stones of any 
species show the effect more markedly than 
the lighter ones. 

The method is rapid and easy — ^it can be 
applied to mounted stones as well as to loose 
ones, and it cannot injure a stone. The student 
should, if possible, obtain the use of a dichro- 
scope and practice with it on all sorts of stones. 
He should especially become -expert in distin- 
guishing between rubies, sapphires, and emer- 
alds, and their imitations. The only imitation 
(scientific rubies and sapphires are not here 
classed as imitations), which is at all likely to 
deceive one who knows how to use the dichro- 
scope is the emerald triplet, made with real 
(but pale) beryl above and below, with a thin 
strip of green glass between. As beryl is 



22 Precious Stones 

doubly refracting to a small degree, and dichroic, 
one might perhaps be deceived by such an 
imitation if not careful. However, the amount 
of dichroism would be less in such a case than 
in a true emerald of as deep a color. 

Those who wish to study further the subject 
of dichroism should see Gem-Stones, by G. F. 
Herbert-Smith, Chapter VII., pp. 53-59, or see 
A Handbook of Precious Stones, by M. D. 
Rothschild, Putnam's, pp. 14-16. 



LESSON V 

SPECIFIC GRA.VITY 

nPHE properties so far considered as serving 
to distinguish precious stones have all 
depended upon the behavior of the material 
toward light. 

These properties were considered first be- 
cause they afford, to those acquainted with 
their use, very rapid and sure means of classi- 
fying precious stones. 

Density of Minerals. We will next consider 
an equally certain test, which, however, re- 
quires rather more time, apparatus, and skill 
to apply. 

Each kind of precious stone has its own den- 
sity. That is, if pieces of different stones were 
taken all of the same size, the weights would 

differ, but like-sized pieces of one and the same 
23 



24 Precious Stones 

material always have the same weight. It is 
the custom among scientists to compare the 
densities of substances with the density of 
water. The number which expresses the rela- 
tion between the density of any substance and 
the density of water is called the specific gravity 
number of the substance. For example, if, 
size for size, a material, say diamond, is 3.51 
times as heavy as water, its specific gravity is 
3.51. It will be seen that since each substance 
always has, when pure, the same specific gravity, 
we have here a means of distinguishing precious 
stones. It is very seldom, if ever, the case that 
we find any two precious stones of the same 
specific gravity. A few stones have nearly 
the same specific gravities, and in such cases 
it is well to apply other tests also. In Jact 
one should always make sure of a stone by seeing 
that two or three different tests point to the same 
species. 

We must next find out how to determine the 
specific gravity of a precious stone. If the 



specific Gravity 25 

shape of a stone were such that the volume 
could be readily calculated, then one could 
easily compare the weight with the voliune or 
with the weight of the same volume of water, 
and thus get the specific gravity (for a specific 
gravity number really tells how much heavier 
a piece of material is than the same volimie of 
water). 

Unfortunately the form of most precious 
stones is such that it would be very difficult 
to calculate the volume from the measurements, 
and the latter would be hard to make accurately 
with small stones. To avoid these difficulties 
the following ingenious method has been devised : 

If a stone is dropped into water it pushes 
aside, or displaces, a body of water exactly 
equal in volume to itself. If the water thus 
displaced were caught and weighed, and the 
weight of the stone then divided by the weight 
of the water displaced, we would have the 
specific gravity number of the stone. 

This is precisely what is done in getting the 



26 



Precious Stones 



specific gravity of small stones. To make sure 
of getting an accurate result for the weight of 
water displaced the following apparatus is used. 
The Specific Gravity Bottle. A small flask- 
like bottle (see Fig. 5) is obtained. This has 




Fig. 5 

A, Flask-like Bottle; B, Indicates Ground Glass Stopper; 

C, Shows Hole Drilled through Stopper 



a tightly fitting ground glass stopper (B). The 
stopper has a small hole (C) drilled through it 
lengthwise. If the bottle is filled with water, 
and the stopper dropped in and tightened, water 
will squirt out through the small hole in the 



specific Gravity 27 

stopper. On wiping off stopper and bottle we 
have the bottle exactly full of water. If now the 
stopper is removed, the stone to be tested (which 
must of course be smaller than the neck of the 
bottle) dropped in, and the stopper replaced, 
exactly as much water will squirt out as is equal 
in 'Volume to the stone that was dropped in. 

If we had weighed the full bottle with the 
stone on the pan beside it, and then weighed the 
bottle with the stone inside it we could now, 
by subtracting the last weight from the first, 
find out how much the water, that was displaced, 
weighed. This is precisely the thing to do. 
The weight of the stone being known we now 
have merely to divide the weight of the stone 
by the weight of the displaced water, and we 
have the specific gravity number. Reference 
to a table of specific gravities of precious stones 
will enable us to name our stone. Such a 
table follows this lesson. 

A Sample Calculation. The actual perform- 
ance of the operation, if one is skilled in 



28 Precious Stones 

weighing, takes less time than it would to read 
this description. At first one will be slow, and 
perhaps one should read and re-read this 
lesson, making sure that all the ideas are clear 
before trying to put them in practice. 

A sample calculation may help make the 
matter clearer, so one is appended : 

Weight of bottle + stone (outside) = 53.51 carats 

Weight of bottle + stone (inside) = 52.51 carats 

Weight of water displaced = i.oo carat 

Weight of stone = 3.51 carats 

Weight of stone 3.51 

Specific gravity = = = 3.51 Sp. g. 

Weight of water i.oo 

In this case the specific gravity being 3.51, 
the stone is probably diamond (see table), but 
might be precious topaz, which has nearly the 
same specific gravity. 

It is assumed that the jeweler will weigh in 
carats, and that his balance is sensitive to .01 
carat. With such a balance, and a specific 
gravity bottle (which any scientific supply house 
will furnish for less than |i) results sufficiently 



Specific Gravity 29 

accurate for the determination of precious 
stones may be had if one is careful to exclude 
air bubbles from the bottle, and to wipe the 
outside of the bottle perfectly dry before each 
weighing. The bottle should never be held in 
the warm hands, or it will act like a thermom- 
eter and expand the water up the narrow tube 
in the stopper, thus leading to error. A hand- 
kerchief may be used to grasp the bottle. 



Table of Specific Gravities of the Principal Gem 

Materials 

Beryl (Emerald) 2.74 

Chrysoberyl (Alexandrite) 3.73 

Corundum (Ruby, sapphire, "Oriental topaz") 4.03 

Diamond 3.52 

Garnet (Pyrope) 3.78 

" (Hessonite) 3.61 

" (Demantoid, known in the trade as "Olivine").. . 3.84 

" (Aknandite) 4.05 

Opal 2.15 

Peridot 3.40 

Quartz (Amethyst, common topaz) 2.66 

Spinel (Rubicelle, Balas ruby) 3.60 

Spodumene (Kunzite) 3.18 

Topaz (precious) 3.53 

Tourmaline ' 3.10 

Turquoise 2.82 

Zircon, lighter variety 4.20 

" heavier variety 4.69 



30 Precious Stones 

For a more complete and scientific discussion 
of specific gravity determination see Gem- 
Stones, by G. F. Herbert-Smith, Chapter VIII., 
pp. 63-77; or see, A Handbook of Precious 
Stones, by M. D. Rothschild, pp. 21-27, for an 
excellent account with illustrations; or see any 
physics text-book. 



LESSON VI 

SPECIFIC GRAVITY DETERMINATIONS 

Weighing a Gem in Water. In the previous 

lesson it was seen that the identity of a precious 

stone may be found by determining its specific 

gravity, which is a number that tells how much 

heavier the material is than a like volume of 

water. It was not explained, however, how 

one would proceed to get the specific gravity of 

a stone too large to go in the neck of a specific 

gravity bottle. In the latter case we resort 

to another method of finding how much a like 

volume of water weighs. If the stone, instead 

of being dropped into a perfectly full bottle of 

water (which then overflows), be dropped into 

a partly filled glass or small beaker of water, 

just as much water will be displaced as though 

the vessel were full, and it will be displaced 

31 



32 Precious Stones 

upward as before, for lack of any other place 
to go. Consequently its weight will tend to 
buoy up or float the stone by trying to get 
back under it, and the stone when in water 
will weigh less than when in air. Anyone who 
has ever pulled up a small anchor when out 
fishing from a boat will recognize at once that 
this is the case, and that as the anchor emerges 
from the water it seems to suddenly grow 
heavier. Not only does the stone weigh less 
when in the water, but it weighs exactly as 
much less as the weight of the water that was 
displaced by the stone (which has a volume 
equal to the volume of the stone) . If we weigh 
a stone first in the air, as usual, and then in 
water (where it weighs less), and then subtract 
the weight in water from the weight in air we 
will have the loss of weight in water, and this 
equals the weight of an equal volume of water, 
which is precisely what we got by our bottle 
method. 

We now need only divide the weight In air 



specific Gravity Determinations 33 

by the loss of weight in water, and we shall 
have the specific gravity of the stone. 




FIG, 6. 

To actually weigh the stone in water we must 
use a fine wire to support the stone. We must 
first find how much this wire itself weighs 
(when attached by a small loop to the hook 
that supports the balance pan and trailing 



34 Precious Stones 

partly in the water, as will be the case when 
weighing the stone in water) . This weight of the 
wire must of course be deducted to get the true 
weight of the stone in water. The beaker of water 
is best supported by a small table that stands over 
the balance pan. One can easily be made out 
of the pieces of a cigar box. (See Fig. 6.) 

The wire that is to support the stone should 
have a spiral at the bottom in which to lay the 
gem, and this should be so placed that the latter 
will be completely submerged at all times, but 
not touching bottom or sides of the beaker. 

Example of data, and calculation, when get- 
ting specific gravity by the method of weighing 
in water: 

Weight of stone = 4.02 carats 

Weight of stone (plus wire) in water =3-32 carats 

Weight of wire = .30 carat 

True weight of stone in water =3.02 carats 

Loss of weight in water = i.oo carat 

Weight of stone 4.02 

Specific gravity = = ■ = 4.02 

Loss in water i.oo 



Specific Gravity Determinations 35 

Here the specific gravity, 4.02 would indi- 
cate some corundum gem (ruby or sapphire), 
and the other characters would indicate at 
once which it was. 

The student who means to master the use 
of the two methods given in Lessons V. and VI. 
should proceed to practice them with stones of 
known specific gravities until he can at least 
get the correct result to the first decimal place. 
It is not to be expected that accurate results 
can be had in the second decimal place, with 
the balances usually available to jewelers. 
When the learner can determine specific gravi- 
ties with some certainty he should then try 
unknown gems. 

The specific gravity method is of especial 
value in distinguishing between the various 
colorless stones, as, for example, quartz crystal, 
true white topaz, white sapphire, white or 
colorless beryl, etc. These are all doubly re- 
fractive, have no color, and hence no dichroism, 
and unless one has a refractometer to get the 



36 Precious Stones 

refractive index, they are difficult to distin- 
guish. The specific gravities are very different, 
however, and readily serve to distinguish them. 
It should be added that the synthetic stones 
show the same specific gravities as their natural 
counterparts, so that this test does not serve 
to detect them. 

Where many gems are to be handled and 
separated by specific gravity determinations, 
perhaps the best way to do so is to have several 
liquids of known specific gravity and to see 
what stones will float and what ones will sink 
in the liquids. Methylene iodide is a heavy 
liquid (sp. g. 3.32), on which a "quartz-topaz," 
for example, sp. g. 2.66, would float, but a true 
topaz, sp. g. 3.53, would sink in it. By dilut- 
ing methylene iodide with benzol (sp. g. 0.88) 
any specific gravity that is desired may be had 
(between the two limits 0.88 and 3.32). Speci- 
mens of known specific gravity are used with 
such liquids and their behavior (as to whether 
they sink or float, or remain suspended in the 



specific Gravity Determinations 37 

liquid,) indicates the specific gravity of the 
liquid. An unknown stone may then be used 
and its behavior noted and compared with 
that of a known specimen, whereby one can 
easily find out whether the unknown is heavier 
or lighter than the known sample. 

An excellent account of the detail of this 
method is given in G. F. Herbert-Smith's Gem- 
Stones, pages 64-71, of Chapter VIII., and 
various liquids are there recommended. It is 
doubtful if the practical gem dealer would find 
these methods necessary in most cases. Where 
large numbers of many different unknown 
gems have to be determined it would pay to 
prepare, and standardize, and use such solutions. 



LESSON VII 

LUSTER AND OTHER REFLECTION EFFECTS 

DY the term luster we refer to the manner 
and degree in which light is reflected 
from the surface of a material. Surfaces of 
the same material, but of varying degrees of 
smoothness would, of course, vary in the vivid- 
ness of their luster, but the type of variation 
that may be made use of to help distinguish 
gems, depends upon the character of the 
material more than upon the degree of smooth- 
ness of its surface. Just as silk has so typical 
a luster that we speak of it as silky luster, and 
just as pearl has a pearly luster, so certain gems 
have peculiar and characteristic luster. The 
diamond gives us a good example. Most 
diamond dealers distinguish between real and 
imitation diamonds at a glance by the character 

38 



Luster and Other Reflection Effects 39 

of the luster. That is the chief, and perhaps 
the only property, that they rely upon for de- 
ciding the genuineness of a diamond, and they 
are fairly safe in so doing, for, with the exception 
of certain artificially decolorized zircons, no 
gem stone is likely to deceive one who is 
fanliliar with the luster of the diamond. It is 
not to be denied that a fine white zircon, when 
finely cut, may deceive even one who is familiar 
with diamonds. The author has fooled many 
diamond experts with an especially fine zircon, 
for the luster of zircon does approach, though 
it hardly equals, that of the diamond. Rough 
zircons are frequently mistaken for diamonds 
by diamond prospectors, and even by pickers 
in the mines, so that some care should be exer- 
cised in any suspicious case, and one should not 
then rely solely on the luster. However, in most 
cases in the trade there is almost no chance of 
the unexpected presence of a zircon and the 
luster test is usually sufficient to distinguish 
the diamond. (Zircons are strongly doubly 



40 Precious Stones 

refractive, as was said in Lesson III. on Double 
Refraction, and with a lens the doubling of the 
back lines may be seen.) 

Adamantine Luster. The luster of a diamond 
is called adamantine (the adjective uses the 
Greek name for the stone itself). It is keen 
and cold and glittering, having a metallic sug- 
gestion. A very large per cent, of the light 
that falls upon the surface of a diamond at any 
low angle is reflected, hence the keenness of its 
luster. If a diamond and some other white 
stone, say a white sapphire, are held so as to 
reflect at the same time images of an incan- 
descent light into the eye of the observer, such 
a direct comparison will serve to show that 
much more light comes to the eye from the 
diamond surface than from the sapphire sur- 
face. The image of the light filament, as seen 
from the diamond, is much keener than as seen 
from the sapphire. The same disparity would 
exist between the diamond and almost any 
other stone. Zircon comes nearest to having 



faster and Other Reflection Effects 41 

adamantine luster of any of the other gems. 
The green garnet that is called "olivine" in the 
trade also approaches diamond in luster, hence 
the name "demantoid," or diamond like, some- 
times applied to it. 

Vitreous Luster. The other stones nearly 
aUJiave what is called vitreous luster (literally, 
glass like), yet owing to difference of hardness, 
and consequent minute differences in fineness 
of surface finish, the keenness of this vitreous 
luster varies slightly in different stones, and a 
trained eye can obtain clues to the identity of 
certain stones by means of a consideration of 
the luster. Garnets, for example, being harder 
than glass, take a keener polish, and a glance at 
a doublet (of which the hard top is usually 
garnet and the base of glass) will show that the 
light is better reflected from the garnet part of 
the top slope than from the glass part. This 
use of luster affords the quickest and surest 
means of detecting a doublet. One can even 
tell a doublet inside a show window, although 



42 Precious Stones 

the observer be outside on the sidewalk, by 
moving to a position such that a reflection from 
the top slope of the stone is to be had. When 
a doublet has a complete garnet top no such 
direct comparison can be had, but by viewing 
first the top luster, and then the back luster, 
in rapid succession, one can tell whether or 
not the stone is a doublet. 

Oily Luster. Certain stones, notably the 
peridot (or chrysolite) and the hessonite (or 
cinnamon stone), have an oily luster. This is 
possibly due to reflection of light that has pene- 
trated the surface slightly and then been 
reflected from disturbed layers beneath the sur- 
face. At any rate, the difference in luster may 
be made use of by those who have trained their 
eyes to appreciate it. Much practice will be 
needed before one can expect to tell at a glance 
when he has a peridot (or chrysolite) by the 
luster alone, but it will pay to spend some spare 
time in studying the luster of the various stones. 

A true, or "precious" topaz, for example, 



Luster and Other Reflection Effects 43 

may be compared with a yellow quartz-topaz, 
and owing to the greater hardness of the true 
topaz, it will be noted that it has a slightly 
keener luster than the other stone, although 
both have vitreous luster. Similarly the corun- 
dum gems (ruby and sapphire), being even 
harder than true topaz, take a splendid surface 
finish and have a very keen vitreous luster. 

Turquoise has a dull waxy luster, due to its 
slight hardness. Malachite, although soft, has, 
perhaps because of its opacity, a keen and 
sometimes almost metallic luster. 

One may note the luster rapidly, without 
apparatus and without damage to the stone. 
We thus have a test which, while it is not con- 
clusive except in a very few cases, will sup- 
plement and serve to confirm other tests, or 
perhaps, if used at first, will suggest what other 
tests to apply. 

Another optical effect that serves to distin- 
guish some stones depends upon the reflec- 
tion of light from within the material due to a 



44 Precious Stones 

certain lack of homogeneity in the substance. 

Cause of Color in the Opal. Thus the opal 
is distinguished by the prismatic colors that 
emerge from it owing to the effect of thin layers 
of material of slightly different density, and 
hence of different refractive index from the 
rest of the material. These thin films act much 
as do soap-bubble films, to interfere with light 
of certain wave lengths, but to reflect certain 
other wave lengths and hence certain colors. 

Again, in some sapphires and rubies are 
found minute, probably hollow, tube-like cavi- 
ties, arranged in three sets in the same positions 
as the transverse axes of the hexagonal crystal. 
The surfaces of these tubes reflect light so as 
to produce a six-pointed star effect, especially 
when the stone is properly cut to a high, round 
cabochon form, whose base is parallel to the 
successive layers of tubes. 

Starstones, Moonstones, Cat's-eye. In the 
moonstone we have another sort of effect, this 
time due to the presence of hosts of small 



Luster and Other Reflection Effects 45 

twin crystal layers that reflect light so as to 
produce a sort of moonlight-on-the-water 
ap-pearance within the stone when the latter is 
properly cut, with the layers of twin crystals 
parallel to its base. Ceylon-cut moonstones 
are frequently cut to save weight, and may 
have to be recut to properly place the layers so 
that the effect may be seen equally over all 
parts of the stone, as set. 

Cat's-eye and tiger's-eye owe their peculiar 
appearance to the presence, within them, of 
many fine, parallel, silky fibers. The quartz 
cat's-eye was probably once an asbestos-like 
mineral, whose soft fibers were replaced by 
quartz in solution, and the latter, while giving 
its hardness to the new mineral, also took up 
the fibrous arrangement of the original material. 
The true chrysoberyl cat's-eye also has a some- 
what similar fibrous or perhaps tubular struc- 
tiu"e. Such stones, when cut en cahochon, show 
a thin sharp line of light running across the cen- 
ter of the stone (when properly cut with the base 



46 Precious Stones 

parallel to the fibers) . This is due to reflection of 
light from the stirf aces of the parallel fibers. The 
line of light runs perpendicularly to the fibers. 

In these cases (opals, starstones, moonstones, 
and cat's-eyes) the individual stone is usually 
easily distinguished from other kinds of stones 
by its peculiar behavior towards light. How- 
ever, it must be remembered that other species 
than corundum furnish starstones (amethyst 
and other varieties of quartz, for example), 
so that it does not follow that any starstone 
is a corundum gem. Also the more valuable 
chrysoberyl cat's-eye may be confused with the 
cheaper quartz cat's-eye unless one is well 
acquainted with the respective appearances of 
the two varieties. Whenever there is any 
doubt other tests should be applied. 

For further account of luster and other types 
of reflection effects see Gem-Stones, by G. F. 
Herbert-Smith, Chapter V., pp. 37-39, or A 
Handbook of Precious Stones, M. D. Rothschild, 
pp. 17, 18. 



LESSON VIII 



HARDNESS 



A NOTHER property by means of which 
one may distinguish the various gems 
from each other is hardness. By hardness 
is meant the abihty to resist scratching. The 
term "hardness" should not be taken to include 
toughness, yet it is frequently so understood 
by the public. Most hard stones are more or 
less brittle and would shatter if struck a sharp 
blow. Other hard stones have a pronounced 
cleavage and split easily in certain directions. 
True hardness, then, implies merely the ability 
to resist abrasion {i. e., scratching). 

Now, not only is hardness very neces- 
sary in a precious stone in order that it may 
receive and keep a fine polish, but the degree 

in which it possesses hardness as compared 

47 



48 Precious Stones 

with other materials of known hardness may 
be made use of in identifying it. 

No scale of absolute hardness has ever come 
into general use, but the mineralogist Mohs 
many years ago proposed the following relative 
scale, which has been used very largely: 

Mohs's Scale of Hardness. Diamond, the 
hardest of all gems, was rated as lo by Mohs. 
This rating was purely arbitrary. Mohs might 
have called it lOO or i with equal reason. It 
was merely in order to represent the different 
degrees of hardness by numbers, that he picked 
out the number lo to assign to diamonds. 
Sapphire (and ruby) Mohs called 9, as being 
next to diamond in hardness. True topaz 
(precious topaz) he called 8. Quartz (amethyst 
and quartz "topaz") was given the number 7. 
Felspar (moonstone) was rated 6, the mineral 
apatite 5, fluorspar 4, calcite 3, gypsum 2, and 
talc I. 

It may be said here that any mineral in 
this series, that is of higher ntmiber than 



Hardness 49 

any other, will scratch the other. Thus dia- 
mond (10) will scratch all the others, sap- 
phire (9) will scratch any but diamond, topaz 
(8) will scratch any but diamond and sapphire, 
and so on. 

It must not be thought that there is any regu- 
larity in the degrees of hardness as expressed 
by these numbers. The intervals in hard- 
ness are by no means equal to the differences 
in number. Thus the interval between dia- 
mond and sapphire, although given but one 
number of difference, is probably greater than 
that between sapphire (9) and talc (i). The 
numbers thus merely give us an order of hard- 
ness. Many gem minerals are, of course, miss- 
ing from this list, and most of the minerals from 
5 down to I are not gem minerals at all. Few 
gem materials are of less hardness than 7, for 
any mineral less hard than quartz (7) will in- 
evitably be worn and dulled in time by the 
ordinary road dust, which contains much 
powdered quartz. 



50 Precious Stones 

In testing a gem for hardness the prob- 
lem consists in finding out which of the above 
minerals is most nearly equal in hardness to the 
unknown stone. Any gem that was approxi- 
mately equal in hardness to a true topaz (8) 
would also be said to be of hardness 8. Thus 
spinel is of about the same hardness as topaz and 
hence is usually rated as 8 in hardness. Simi- 
larly opal, moonstone, and turquoise are of 
about the same hardness as felspar and are all 
rated 6. 

Frequently stones will be found that in 
hardness are between some two of Mohs's min- 
erals. In that case we add one half to the 
number of the softer mineral; thus, peridot, 
benitoite, and jade (nephrite) are all softer than 
quartz (7) but harder than felspar (6) ; hence we 
say they are 6}i in hardness. Beryl (aqua- 
marine and emerald), garnet (almandine), 
and zircon are rated 7>^ in hardness, be- 
ing softer than true topaz but harder than 
quartz. A table of the hardness of most of 



Hardness 51 

the commonly known gem-stones follows this 
lesson. 

Having now an idea of what hardness means 
and how it is expressed, we must next inquire 
how one may make use of it in identifying 
unknown gems. 

How to Apply the Hardness Test. In the first 
place, it is necessary to caution the beginner 
against damaging a fine gem by attempting to 
test its hardness in any but the most careful 
manner. The time-honored file test is really a 
hardness test and serves nicely to distinguish 
genuine gems, of hardness 7 or above, from 
glass imitations. A well-hardened steel file is 
of not quite hardness 7, and glass of vari- 
ous types while varying somewhat averages 
between 5 and 6. Hence, glass imitations 
are easily attacked by a file. To make the 
file test use only a very fine file and apply it with 
a light but firm pressure lengthwise along the 
girdle (edge) of the unset stone. If damage 
results it will then be almost unnoticeable. 



53 Precious Stones 

Learn to know the feel of the file as it 
takes hold of a substance softer than itself. 
Also learn the sound. If applied to a hard 
stone a file will slip on it, as a skate slips on 
ice. It will not take hold as upon a softer 
substance. 

If the stone is set, press a sharp corner 
of a broken-ended file gently against a back 
facet, preferably high up toward the girdle, 
where any damage will not be visible from the 
front, and move the file very slightly along the 
surface, noting by the feel whether or not it 
takes hold and also looking with a lens to see if 
a scratch has been made. Do not mistake a 
line of steel, left on a slightly rough surface, for 
a true scratch. Frequently on an unpolished 
girdle of real gem material the file will leave 
a streak of steel. Similarly when using test 
minerals in accordance with what follows do not 
mistake a streak of powder from the yielding 
test material, for a true scratch in the material 
being tested. The safe way is to wipe the spot 



Hardness 53 

thus removing any powder. A true scratch 

will, of course, persist. 

A doublet, being usually constructed 
of a garnet top and a glass back, may 
resist a file at the girdle if the garnet 
top covers the stone to the girdle, as is 
somStimes the case, especially in the smaller 
sizes. In this case the back must be 
tested. 

One should never pass a file rudely across 
the corners or edges of the facets on any stone 
that may be genuine, as such treatment really 
amounts to a series of light hammer blows, and 
the brittleness of most gem stones would cause 
them to yield, irrespective of their hardness. 
It should be remembered that some genuine 
stones are softer than a file, so that it will not 
do to reject as worthless any material that is 
attacked by a file. Lapis lazuli (5), sphene 
(5), opal (6), moonstone (6), amazonite (6), 
turquoise (6), peridot (6^), demantoid garnet 
(6/^) (the "olivine" of the trade), and jade 



54 Precious Stones 

(nephrite) (6>^), are all more or less attacked 
by a file. 

Table of Hardness of the Principal Gem-Stones 

10. Diamond. 
g}4. (Carborundum.) 
9. Sapphire and ruby (also all the color varieties of 

sapphire). 
8}4. Chrysoberyl (alexandrite). 
8. True topaz and spinel (rubicelle, balas ruby). 
7X» Emerald, aquamarine, beryl, Morganite, zircon 

(jacinth and true hyacinth and jargoon), almandine 

garnet. 
7^. Pyrope garnet (Arizona ruby, cape ruby), hessonite 

garnet (cinnamon stone), tourmaline (various 

colors vary from 7 to 7>^), kunzite (7+) 
7. Amethyst, various quartz gems, quartz "topaz," 

jade (jadeite). 
6}4. Peridot (chrysolite), demantoid garnet ("olivine"), 

jade (nephrite). 
6. Opal, moonstone, turquoise. 
5. Lapis lazuli. 



LESSON IX 
BARDNESS— Continued 

Minerals Used in Testing Hardness. For 

testing stones that are harder than a file the 
student should provide himself with the follow- 
ing set of materials: 

1. A small crystal of carborundum. (Most 
hardware stores have specimen crystals as 
attractive advertisements of carborundum as 
an abrasive material, or the Carborundum Co., 
Niagara Falls, N. Y., will supply one.) 

2. A small crystal of sapphire (not of gem 
quality, but it should be transparent and 
compact. A pale or colorless Montana sap- 
phire can be had for a few cents of any mineral 
dealer). 

3. A small true topaz crystal. (The pure 

white topaz of Thomas Mountain, Utah, is 

55 



56 Precious Stones 

excellent; or white topaz from Brazil or Japan 
or Mexico or Colorado will do. Any mineral 
house can furnish small crystals for a few 
cents when not of specially fine crystalliza- 
tion.) 

4. A small quartz crystal. (This may be 
either amethyst or quartz-topaz or the common 
colorless variety. The fine, sharp, colorless 
crystals from Herkimer County, N. Y., are 
excellent. These are very inexpensive.) 

5. A fragment of a crystal of felspar. (Com- 
mon orthoclase felspar, which is frequently 
of a brownish pink or flesh color, will do.) 

These five test stones represent the fol- 
lowing degrees of hardness: 

I. Carborundum is harder than any gem 
material but diamond. It will scratch sap- 
phire and ruby, which are rated 9 in hardness, 
hence we may call carborundum ()}4 if we wish. 
It is, however, very much softer than diamond, 
and the latter will scratch it upon the slightest 
pressure. 



Hardness 57 

2. Sapphire, of hardness 9, scratching any 
gem material except diamond. 

3. True topaz, of hardness 8. It is scratched 
by sapphire (and, of course, ruby), also by 
chrysoberyl (which is hence rated S)4), but 
scratches most other stones. Spinel (which 
is also rated as 8 in hardness) is really a bit 
harder than topaz. 

4. Quartz, of hardness 7, and scratched 
by all the previous stones but scratching 
those that were listed above as of less hardness 
than a file. 

5. Felspar, of hardness 6, hence slightly 
softer than a file and yielding to it, but scratch- 
ing the stones likewise rated as 6 when applied 
forcibly to them. Also scratching stones rated 
as less than 6 on slight pressure. 

We must next consider how these minerals 
may be safely used upon gem material. Obvi- 
ously it would be far safer to use them upon 
rough gem material than upon cut stones. 
However, with care and some little skill, one 



58 Precious Stones 

may make hardness tests without particular 
danger to fine cut material. 

The way to proceed is to apply the cut 
stone (preferably its girdle, or if that is so 
set as not to be available, a comer where 
several facets meet) gently to the flat sur- 
face of one of the softer test stones, draw- 
ing it lightly along the surface and noting 
the feel and looking to see if a scratch results. 
If the test stone is scratched try the next 
harder test stone similarly. Do not attempt 
to use the test stone upon any valuable cut stone. 
Proceed as above until the gem meets a test 
stone that it does not attack. Its hardness 
is then probably equal to the latter and perhaps 
if pressed forcibly against it a slight scratch 
would result, but it is not advisable to resort to 
heavy pressure. A light touch should be culti- 
vated in this work. Having now an indication 
as to the hardness of the unknown gem look 
up in the table of the previous lesson those 
gems of similar hardness and then by the 



Hardness 59 

use of some of the tests already given decide 
which of the stones of that degree of hardness 
you have. Never rely upon a single test in identi- 
fying a gem. 

For further study of hardness and its use 
in testing gems see Gem-Stones, G. F. Herbert- 
Smith, Chap IX., pp. 78-81, and table on 
P- 305 ; or see A Handbook of Precious Stones, 
Rothschild, pp. 19, 20, 21. 



LESSON X 

DISPERSION 

A NOTHER property which may be made 
use of in deciding the identity of certain 
gems is that called dispersion. We have seen in 
Lesson II. that light in entering a stone from 
the air changes its path (refraction), and in 
Lesson III. it was explained that many minerals 
cause light that enters them to divide and pro- 
ceed along two different paths (double refrac- 
tion). Now it is further true that light of 
the various colors (red, orange, yellow, green, 
blue, and violet) is refracted variously — the 
violet being bent most sharply, the red least, 
and the other colors to intermediate degrees. 
The cut (Fig. 7) represents roughly and in an 
exaggerated manner the effect we are discussing. 

Now in a cut stone this separation of light 
60 



Dispersion 6i 

of different colors, or dispersion of light, as it 
is called, results in the reflection of each of the 
colors separately from the steep sloping back 
facets of the stone. If almost any clear, 
colorless faceted stone is placed in the sunlight 




Y.B.6Y.0JI 

Fig. 7. 

• 

and a card held before it to receive the reflec- 
tions, it will be seen that rainbow-like reflections 
appear on the card. These spectra, as they are 
called, are caused by the dispersion of light. 
With a diamond the spectra will be very bril- 
liant and of vivid coloring, and the red will 
be widely separated from the blue. With white 
sapphire or white topaz, or with rock crystal 
(quartz), the spectra will be less vivid — they 



62 Precious Stones 

will appear in pairs (due to the double 
refraction of these minerals), and the red 
and blue will be near together (i. e., the 
spectra will be short). This shortness in the 
latter cases is due to the small dispers'ive 
power of the three minerals mentioned. 
Paste (lead glass) gives fairly vivid spectra, 
and they are single like those from diamond, 
as glass is singly refracting. The dispersion 
of the heavy lead glass approaches that of 
diamond. The decolorized zircon (jargoon) has 
a dispersion well up toward that of diamond 
and gives fairly vivid spectra on a card, but 
they are double, as zircon is doubly refracting. 
Sphene (a gem rarely seen in the trade) and 
the demantoid garnet (a green gem often called 
"olivine" in the trade) both have very high 
dispersive power, exceeding the diamond in this 
respect. As they are both colored stones 
(sphene is usually yellowish, sometimes greenish 
or brown), the vividness of their color-play is 
much diminished by absorption of light within 



Dispersion 63 

them. So also the color-play of a deeply- 
colored fancy diamond is diminished by absorp- 
tion. 
Dispersion as a Test of the Identity of a Gem. 

We may now consider how an acquaintance 
with the dispersive powers of the various stones 
can fee used in distinguishing them. If a stone 
has high dispersive power it will exhibit "fire, " 
as it is called — i. e., the various colors will be so 
widely separated within the stone, and hence 
reflected out so widely separated, that they will 
fall on the eye (as on the card above) in separate 
layers, and vivid flashes of red or yellow or 
other colors will be seen. Such stones as the 
white sapphire (and others of small disper- 
sion), however, while separating the various 
colors appreciably as seen reflected on a card, 
do not sufliciently separate them to produce 
the "fire" effect when the light falls on the eye. 
This is because the various colors, being very 
near together in this case, cross the eye so 
rapidly, when the stone is moved, that they 



64 Precious Stones 

blend their effect and the eye regards the light 
that thus falls upon it as white. We have here 
a ready means of distinguishing the diamond 
from most other colorless gems. The trained 
diamond expert relies (probably unconsciously) 
upon the dispersive effect (or "fire") nearly as 
much as upon the adamantine luster, in telling 
at a glance whether a stone is or is not a diamond. 
Of all colorless stones, the only one likely to 
mislead the expert in this respect is the whitened 
zircon (jargoon), which has almost adamantine 
luster and in addition nearly as high dispersive 
power as diamond. However, zircon is doubly 
refracting (strongly so), and the division of the 
spectra which results (each facet producing 
two instead of only one) weakens the "fire" so 
that even the best zircon is a bit "sleepy" as 
compared with even an ordinary diamond. 

In addition to providing a ready means of 
identifying the diamond, a high degree of dis- 
persion in a stone of pronounced color would 
lead one to consider sphene, demantoid garnet 



Dispersion 65 

(if green), and zircon (which might be reddish, 
yellowish, brown, or of other colors), and if the 
stone did not agree with these in its other 
properties one should suspect glass. 

A good way to note the degree of dispersion, 
aside from the sunlight-card method, is to look 
at the stone from the back while holding it up 
to the light (daylight). Stones of high disper- 
sive power will display vivid color play in this 
position. Glass imitations of rubies, emeralds, 
amethysts, etc., will display altogether too 
much dispersion for the natural gems. 

In Chap. III., p. 20, of G. F. Herbert-Smith's 
Gem-Stone's, a brief account of dispersion is 
given. College text-books on physics also treat 
of it, and the latter give an account of how 
dispersion is measured and what is meant by a 
coefficient of dispersion. Most gem books say 
little about it, but as we have seen above, a 
knowledge of the matter can, when supple- 
mented by other tests, be applied practically in 
distinguishing gems. 



LESSON XI 



COLOR 



TN reserving to the last the property of color, 
which many dealers in gems use first when 
attempting to identify a precious stone, I have 
sought to point out the fact that a determina- 
tion based solely upon color is very likely to be 
wrong. So many mineral species are found in 
so many different colors that to attempt to 
identify any mineral species by color alone 
is usually to invite disaster. The emerald, 
alone among gems, has, when of fine color, a 
hue that is not approached by any other species. 
The color of the grass in the springtime fitly 
describes it. Yet even here the art of man has 
so closely counterfeited in glass the green of the 
emerald that one cannot be sure of his stone by 
color alone. As was suggested earlier in these 

66 



Color 67 

lessons, the writer has several times recently 
had occasion to condemn as glass imitations 
stones for which high prices had been paid as 
genuine emeralds, those who sold them having 
relied solely upon a trained eye for color. 

Confusion of Gems Due to Similarity of Color. 
Thte same tendency to rely upon color causes 
many in the trade to call all yellow stones 
"topaz" whether the species be corundum 
(oriental topaz), true topaz (precious topaz), 
citrine quartz (quart topaz), heliodor (yellow 
beryl), jacinth (yellow zircon), or what not. 

Similarly the public calls all red stones ruby. 
Thus we have "cape ruby" and "Arizona 
ruby" (pyrope garnet), "spinel ruby" (more 
properly ruby spinel), "Siam ruby" (very 
dark red corundum), "Ceylon ruby" (pale 
pinkish corundum), rubellite (pink tourmaline), 
and lastly Burmah ruby (the fine blood-red 
corundum) . 

While it is true that color, unless skillfully 
estimated and wisely used in conjunction with 



68 Precious Stones 

other properties, is a most unreliable guide, 
yet when thus used, it becomes a great help 
and serves sometimes to narrow down the chase, 
at the start, to a very few species. To thus 
make use of it requires an actual acquaintance 
with the various gem materials, in their usual 
colors and shades and an eye trained to note and 
to remember minute differences of tint and 
shade. The suggestions which follow as to 
usual colors of mineral species must then be 
used only with discretion and after much faith- 
ful study of many specimens of each of the 
species. 

Let us begin with the beginning color of the 
visible spectrum, red, and consider how a close 
study of shades of red can help in distinguishing 
the various red stones from each other. In the 
first place we will inquire what mineral species 
are Hkely to furnish us with red stones. Omit- 
ting a number of rare minerals, we have (i) 
corundum ruby, (2) garnet of various types, 
(3) zircon, (4) spinel, (5) tourmaline. These five 



Color 69 

minerals are about the only common species 
which give us an out-and-out red stone. 
Let us now consider the distinctions between 
the reds of these different species. The red 
of the ruby, whether dark (Siam type), blood 
red (Burmah type), or pale (Ceylon), is more 
pissing usually than the red of any of the 
other species. Viewed from the back of the 
stone (by transmitted light) it is still pleasing. 
It may be purplish, but is seldom orange red. 
Also, owing to the dichroism of the ruby the 
red is variable according to the changing posi- 
tion of the stone. It therefore has a certain 
life and variety not seen in any of the others 
except perhaps in red tourmaline, which, how- 
ever, does not approach ruby in fineness of red 
color. 

Red Stones of Similar Shades. The garnet, 
on the other hand, when of fire-red hue, is darker 
than any but the Siam ruby. It is also more 
inclined to orange red or brownish red — and the 
latter is especially true when the stone is seen 



70 Precious Stones 

against the light (by transmitted Hght). Its 
color then resembles that of a solution of " iron " 
such as is given as medicine. The so-called 
"ahnandine" garnets (those of purplish red 
tint) do not equal the true 'ruby in brightness 
of color and when held up to the light show 
more prismatic colors than the true ruby, 
owing to the greater dispersion of garnet. 
The color also lacks variety (owing to lack 
of dichroism). While a fine garnet may make 
a fair-looking "ruby" when by itself, it looks 
inferior and dark when beside a fine ruby. By 
artificial light, too, the garnet is dark as com- 
pared with the true ruby, and the latter shows 
its color at a distance much more strongly than 
the garnet. 

The red zircon, or true hyacinth, is rare. 
(Many hessonite garnets are sold as hyacinths 
in the trade. These are usually of a brownish 
red.) The red of the hyacinth is never equal to 
that of the ruby. It is usually more somber, and 
a bit inclined to a brownish cast. The disper- 



Color 71 

sion of zircon, too, is so large (about 87 per cent, 
of that of diamond) that some little "color- 
play" is likely to appear along with the intrinsic 
color. The luster too is almost adamantine 
while that of ruby is softer and vitreous. Al- 
though strongly doubly refracting, the hyacinth 
shews scarcely any dichroism and thus lacks 
variety of color. Hence a trained eye will at 
once note these differences and not confound 
the stone with ruby. 

Spinels, when red, are almost always more 
yellowish or more purplish than fine corundum 
rubies. They are also singly refracting and 
hence exhibit no dichroism and therefore lack 
variety of color as compared with true ruby. 
Some especially fine ones, however, are of a good 
enough red to deceive even jewelers of experi- 
ence, and one in particular that I have in 
mind has been the rounds of the stores and 
has never been pronounced a spinel, although 
several "experts" have insisted that it was a 
scientific ruby. The use of a dichroscope would 



72 Precious Stones 

have saved them that error, for the stone is 
singly refracting. Spinels are usually clearer 
and more transparent than garnets and show 
their color better at a distance or when in a poor 
Hght. 

Tourmaline of the reddish variety (rubellite) 
is seldom of a deep red. It is more inclined 
to be pinkish. The dichroism of tourmaline 
is stronger than that of ruby and more obvious 
to the unaided eye. The red of the rubellite 
should not deceive anyone who has ever seen a 
fine corundimi ruby. 

YELLOW STONES 

Considering next the stones of yellow color, 
we have the following species to deal with: 
(i) diamond, (2) corundum, (3) precious topaz, 
(4) quartz, (5) beryl, (6) zircon, (7) tourmaline. 

Yellow Zircon Resembles Yellow Diamond. 
Here we have less opportunity to judge of 
the species by the color than was the case with 



Color 73 

the red stones. The diamond, of course, is 
easy to tell, not by the kind of yellow that it 
displays, for it varies greatly in that respect, but 
rather by its prismatic play blended with the 
intrinsic color. Its luster also gives an imme- 
diate clue to its identity. It is necessary, how- 
ever to be sure that we are not being deceived 
by a yellow zircon, for the latter has considerable 
"fire" and a keen luster. Its strong double 
refraction and its relative softness, as well as its 
great density will serve to distinguish it. Of the 
other yellow stones, the true or precious topaz 
is frequently inclined to a pinkish or wine yel- 
low and many such stones lose all their yellow 
(retaining their pink) when gently heated. 
The so-called "pinked" topazes are thus pro- 
duced. 

The yellow corundimi rarely has a color 
that is at all distinctive. As far as color 
goes the material might be yellow quartz, 
or yellow beryl, or yellow zircon, or yellow 
tourmaline (Ceylon type). Many of the 



74 Precious Stones 

yellowish tourmalines have a decidedly green- 
ish cast (greenish yellow chrysoberyl might 
resemble these also). However, in general if 
one has a yellow stone to determine it will be 
safer to make specific gravity or hardness tests, 
or both, before deciding, rather than to rely 
upon color. 



LESSON XII 
COLOR — Coniinued 

GREEN STONES 

T ET US first consider what mineral species 
are most likely to give us green stones. 
Omitting the semi-precious opaque or trans- 
lucent stones we have: 

1. Grass-green beryl (the emerald) which is, 
of course, first in value among the green stones 
and first in the fine quality of its color. 

2. Tourmaline (some specimens of which 
perhaps more nearly approach the emerald 
than any other green stones). 

3. The demantoid garnet (sometimes called 
"olivine" in the trade). 

4. True olivine (the peridot and the chryso- 
lite of the trade). 

75 



76 Precious Stones 

5. Bluish green beryl (aquamarine). 

6. Green sapphire (Oriental emerald or 
Oriental aquamarine). 

7. Chrysoberyl (alexandrite and also the 
greenish yellow chrysoberyl). 

I. Considering first the emerald, we have 
as legitimate a use of color in distinguishing 
a stone as could be selected, for emerald of fine 
grass-green color is not equaled by any other 
precious stone in the rich velvety character of 
its color. We have to beware here, however, of 
the fine glass imitations, which, while lacking 
the variety of true emerald, because of lack of 
dichroism, are nevertheless of a color so nearly 
like that of the emerald that no one should 
attempt to decide by color alone as to whether 
a stone is genuine or imitation emerald. If a 
hardness test shows that the material is a genu- 
ine hard stone and not a paste, then one who is 
well accustomed to the color of fine emerald can 
say at once whether a stone is a fine emer- 
ald or some other hard green stone. Where 



Color 77 

the color is less fine, however, one might 
well refuse to decide by the color, even when 
sure that the material is not glass, for some 
fine tourmalines approach some of the poorer 
emeralds in richness of color. 

The "Scientific Emerald" Fraud. No 
"scientific" emeralds of marketable size have 
ever been produced as far as can be learned. 
Many attempts to reproduce emerald by 
melting beryl or emerald of inferior color have 
resulted only in the production of a beryl glass, 
which, while its color might be of desirable 
shade, was softer and lighter in weight than 
true emerald. It was also a true glass and 
hence singly refracting and without dichroism, 
whereas emerald is crystalline (not glassy or 
amorphous), is doubly refracting, and shows 
dichroism. 

Do not be misled, then, into buying or 
selling an imitation of emerald under the 
terms "synthetic," "scientific," or "recon- 
structed," as such terms, when so used, are 



78 Precious Stones 

used to deceive one into thinking that the 
product offered bears the same relation to 
the true emerald that scientific rubies and 
sapphires bear to the natural stones. Such 
is not the case. 

About the most dangerous imitation of the 
emerald that is ever seen in the trade is the trip- 
let that has a top and a back made of true but 
pale beryl (the same mineral as emerald, but 
not of the right color) and a thin slice of 
deep emerald green glass laid between. This 
slice of glass is usually placed behind the 
girdle so that a file will not find any point 
of attack. The specific gravity of the trip- 
let is practically that of emerald, its color 
is often very good, and it is doubly refracting. 
It is thus a dangerous imitation. (See Fig. 8.) 

Emerald Triplets, A careful examination of 
one of these triplets, in the unset condition, 
with a good lens, will reveal the thin line of 
junction of the beryl with the glass. (The 
surface lusters of the two materials are enough 



Color 79 

different for the trained eye to detect the margin 
at once.) Such a triplet, if held in the sun, will 
reflect onto a card two images in pale or white 
light, one coming from the top surface of the 
table and the other from the top surface of 




0££P G/e££A/ 

CL/135 o/i pjjsre 

P^L£ B6RYL 



flG. 8. — EMERALD_TRIPLET. 

the glass slice within. In other words, it acts 
in this respect like a doublet. A true emerald 
would give only one such reflection, which 
would come from the top surface of the 
table. 

2. ToiuTQalines, when green, are usually 
darker than emeralds and of a more pro- 
nounced yellow green, or they may be of 
too bluish a green, as is the case with some 
of the finest of the green tourmalines from 



8o Precious Stones 

Maine. Connecticut green tourmaline tends 
more to the dark yellowish green, and Ceylon 
tourmaline to the olive green. The stronger 
dichroism of the tourmaKne frequently reveals 
itself to the naked eye, and there is usually 
one direction or position in which the color 
of the stone is very inferior to its color in the 
opposite direction or position. Most tourma- 
lines (except the very lightest shades) must 
be cut so that the table of the finished stone 
lies on the side of the crystal, as, when cut with 
the table lying across the crystal (perpendicular 
to the principal optical axis) the stones are 
much too dark to be pretty. Hence when one 
turns the cut stone so that he is looking in the 
direction which was originally up and down 
the crystal (the direction of single refraction 
and of no dichroism) he gets a glimpse of a 
less lovely color than is furnished by the 
stone in other positions. With a true emerald 
no such disparity in the color would appear. 
There might be a slight change of shade (as 



Color 8i 

seen by the naked eye), but no trace of an ugly 
shade would appear. 

By studying many tourmalines and a few 
emeralds one may acquire an eye for the differ- 
ences of color that characterize the two stones, 
but' it is still necessary to beware of the fine 
glas*- imitation and to use the file and also to 
look with a high-power glass for any rounding 
bubbles. The emerald will never have the lat- 
ter. The glass imitation frequently does have 
them. The sharp jagged flaws and cracks that 
so often appear in emerald are likely to appear 
also in tourmaline as both are brittle materials. 
The glass imitations frequently have such flaws 
put into them either by pinching or by striking 
the material. Frequently, too, wisps of tiny 
air bubbles are left in the glass imitations in 
such fashion that unless one scrutinizes them 
carefully with a good lens they strongly resem- 
ble the flaws in natural emerald. 

I have thus gone into detail as to how one 
may distinguish true emerald from tourmaline 



82 Precious Stones 

and from glass imitations because, on account of 
the high value of fine emerald and its infrequent 
occurrence, there is perhaps more need for the 
ability to discriminate between it and its imi- 
tations and substitutes than there is in almost 
any other case. Where values are high the 
temptation to devise and to sell imitations 
or substitutes is great and the need for skill in 
distinguishing between the real and the false 
is proportionally great. 

3. The demantoid garnet (often unfor- 
tunately and incorrectly called "olivine" in 
the trade) is usually of an olive or pistachio 
shade. It may, however, approach a pale 
emerald. The refraction being single in this, 
as in all garnets, there is little variety to the 
color. The dispersion being very high, how- 
ever, there is a strong tendency, in spite of the 
depth of the body color, for this stone to dis- 
play "fire, " that is, rainbow color effects. The 
luster, too, is diamond-like as the name "de- 
mantoid" signifies. With this account of the 



Color 83 

stone and a few chances to see the real deman- 
toid garnet beside an emerald no one would 
be likely to mistake one for the other. 
The demantoid garnet is also very soft as 
compared with emerald {6}4 as against 
nearly 8). 

4.* True olivine (the peridot or the chryso- 
lite of the trade) is of a fine leaf -green or bottle- 
green shade in the peridot. The chrysolite of 
the jeweler is usually of a yellower green. 
Frequently an olive-green shade is seen. The 
luster of olivine (whether of the peridot shade 
or not) is oily, and this may serve to distinguish 
it from tourmaline (which it may resemble 
in color). Its double refraction is very large 
also, so that the doubling of the edges of the 
rear facets may easily be seen through the table 
with a lens. The dichroism is feeble too, 
whereas that of tourmaline is strong. No 
one would be likely to confuse the stone 
with true emerald after studying what has 
preceded. 



84 Precious Stones 

5. Bluish green beryl (aquamarine) is usu- 
ally of a pale transparent green or blue green 
(almost a pure pale blue is also found). 

Having all the properties of its more valuable 
variety, emerald, the pale beryl may, by the 
use of these properties, be distinguished from 
the pale blue-green topaz which so strongly 
resembles it in color. 

6, Green sapphire seldom even approaches 
emerald in fineness of color. When it remotely 
suggests emerald it is called "Oriental" emerald 
to denote that it is a corundum gem. Most 
green sapphires are of too blue a green to re- 
semble emerald. Some are really "Oriental" 
aquamarines. In some cases the green of the 
green sapphire is due to the presence, within 
the cut stone, of both blue and yellow portions, 
the Hght from which, being blended by its re- 
flection within the stone, emerges as green as 
seen by the unaided eye, which cannot analyze 
colors. The dark sapphires of Australia are 
frequently green when cut in one direction and 



Color 85 

deep blue when cut in the opposite direction. 
The green, however, is seldom pleasing. 

7. Chrysoberyl as usually seen is of a yel- 
lowish green. The fine gem chrysoberyls known 
as alexandrites, however, have a pleasing bluish 
green or deep olive green color by daylight 
and 'change in a most surprising fashion by 
artificial light under which they show raspberry 
red tints. This change, according to G. F. 
Herbert-Smith, is due principally to the fact 
that the balance in the spectrum of light trans- 
mitted by the stone is so delicate that when a 
light, rich in short wave lengths, falls upon 
it the blue green effect is evident, whereas 
when the light is rich in long wave lengths 
(red end of the spectrum), the whole stone 
appears red. The strong dichroism of the 
species also aids this contrast. The chrysoberyls 
of the cat's-eye type (of fibrous or tubular in- 
ternal structure) are usually of olive green or 
brownish green shades. 

Those who wish to further study color dis- 



86 Precious Stones 

tinctions in green stones are recommended 
to see the chapters on beryl (pp. 184-196), 
peridot (pp. 225-227), corundum (pp. 172-183), 
tourmaline (pp. 219-224), chrysoberyl (pp. 
233-237), and garnet (demantoid, pp. 216- 
218) in G. F. Herbert-Smith's Gem-Stones. 



LESSON XIII 
COLOR — Contimced 

BLUE STONES 

nnHE species that furnish blue stones in 
sufficient number to deserve considera- 
tion are, aside from opaque stones: 

1. Corundum (sapphire). 

2. Spinel. 

3. Tourmaline. 

4. Topaz. 

5. Diamond. 

6. Zircon. 

I. Of these minerals the only species that 

furnishes a fine, deep velvety blue stone is 

the corundum, and fine specimens of the 

cornflower blue variety are very much in- 

demand and command high prices. The color 

87 



88 Precious Stones 

in sapphires ranges from a pale watery blue 
through deeper shades (often tinged with green) 
to the rich velvety cornflower blue that is so 
much in demand, and on to dark inky blues that 
seem almost black by artificial light. Most 
sapphires are better daylight stones than 
evening stones. Some of the sapphires from 
Montana, however, are of a bright electric blue 
that is very striking and brilliant by artificial 
Hght. 

How Sapphires should be Cut. The direction 
in which the stone is cut helps determine the 
quality of the blue color, as the "ordinary" 
ray (sapphire exhibits dichroism) is yellowish 
and ugly in color, and if allowed to be con- 
spicuous in the cut stone, its presence, blending 
with the blue, may give it an undesirable green- 
ish cast. Sapphires should usually be cut so 
that the table of the finished stone is per- 
pendicular to the principal optical axis of 
the crystal. Another way of expressing this 
fact is that the table should cross the long axis 



Color 89 

of the usual hexagonal crystal of sapphire, at 
right angles. This scheme of cutting puts the 
direction of single refraction up and down the 
finished stone, and leaves the ugly ordinary 
rays in poor position to emerge as the light that 
falls upon the girdle edges cannot enter and 
croSB the stone to any extent. 

To find out with a finished stone whether 
or not the lapidary has cut it properly as re- 
gards its optical properties one may use the 
dichroscope, and if there is little or no dichroism 
in evidence when looking through the table 
of the stone it is properly cut. 

Where a sapphire shows a poor color and 
the dichroscope shows that the table was laid 
improperly, there is some possibility of im- 
proving the color by recutting to the above 
indicated position. However, one must use 
much judgment in such a case, as sapphires, 
like other corundum gems, frequently have 
their color irregularly distributed, and the 
skillful lapidary will place the culet of the stone 



90 Precious Stones 

in a bit of good color, and thus make the whole 
stone appear to better advantage. It would not 
do to alter such an arrangement, as one would 
get poorer rather than better color by recutting 
in such a case. 

While some of the blue stones about to 
be described may resemble inferior sapphires, 
none of them approaches the better grades of 
sapphire in fineness of blue coloration. The 
scientific sapphire, of course, does approach 
and even equals the natural sapphire so that 
one must know how to distinguish between 
them. This distinction is not one of color, 
however, and it will be separately considered 
a little later. 

2. Blue spinels are infrequently seen in 
commerce. They never equal the fine sap- 
phire in their color, being more steely. They, 
of course, lack dichroism and are softer than 
sapphire as well as lighter. 

3. Blue tourmalines are never of fine 
sapphire blue. The name indicolite which 



Color 91 

mineralogists give to these blue stones sug- 
gests the indigo blue color which they afford. 
The marked dichroism of tourmaline will also 
help detect it. Some tourmalines from Brazil 
are of a lighter shade of blue and are sometimes 
called "Brazilian sapphires." 

4,- Blue topaz is usually of a pale sky 
blue or greenish blue and is likely to be con- 
fused with beryl of similar color. The high 
density of topaz (3.53) as compared with beryl 
(2.74) serves best to distinguish it. 

" Fancy " Blue Diamonds. 5. Blue dia- 
monds are usually of very pale bluish or violet 
tint. A few deeper blue stones are seen occa- 
sionally as "fancy" diamonds. These are sel- 
dom as deep blue as pale sapphires. Even the 
famous Hope Blue Diamond, a stone of about 
forty-four carats and of great value, is said to 
be too light in color to be considered a fine 
sapphire blue. Some of the deeper blue dia- 
monds have a steely cast. The so-called blue- 
white stones are rarely blue in their body color, 



92 Precious Stones 

but rather are so nearly white that the blue 
parts of the spectra which they produce are 
very much in evidence, thus causing them 
to face up blue. There is little likelihood of 
mistaking a bluish diamond for any other 
stone on account of the "fire" and the ada- 
mantine luster of the diamond. 

6. Blue zircon, however, has nearly ada- 
mantine luster and considerable fire. The 
color is usually sky blue. Such stones are 
seldom met with in the trade. 

For a more detailed account of the vari- 
ous blue stones see G. F. Herbert-Smith's 
Gem-Stones, as follows: 

For sapphires, pp. 172-173, 176, 182; for 
spinel, pp. 203, 204, 205; for tourmaline, pp. 
220, 221, 223; for topaz, pp. 198, 200, 201; 
for diamond, pp. 130, 136, 170, and for zircon, 
pp. 229, 231. 



LESSON XIV 
COLOR — Concluded 

PINK, PURPLE, BROWN, AND COLORLESS STONES 

Pink Stones. Pink stones are yielded by (i) 
corundum (pink sapphire), (2) spinel (balas 
ruby), (3) tourmaline (rubellite), (4) true topaz 
(almost always artificially altered), (5) beryl 
(morganite), (6) spodumene (kunzite), and (7) 
quartz (rose-quartz). 

These pink minerals are not easily dif- 
ferentiated by color alone, as the depth and 
quality of the pink vary greatly in differ- 
ent specimens of the same mineral and in 
the different minerals. There is dichroism 
in the cases of pink sapphire, pink tourma- 
line (strong), pink topaz (strong), pink beryl 
(less pronounced), and kunzite (very marked 
and with a yellowish tint in some directions that 

93 



94 Precious Stones 

contrasts with the beautiful violet tint in 
another direction in the crystal). Pink quartz 
is almost always milky, and shows little dichro- 
ism. Pink spinel is without dichroism, being 
singly refracting. Hardness and specific gravity 
tests will best serve to distinguish pink stones 
from each other. The color alone is not a safe 
guide. 

Purple Stones. Among the mineral species 
that furnish purple stones, (i) quartz is pre- 
eminent in the fineness of the purple color. 
Such purple stones are, of course, known as 
amethysts. After quartz come (2) corundum 
(Oriental amethyst), (3) spinel (almandine 
spinel), (4) garnet (almandine), and (5) spodu- 
mene (variety kunzite). 

The purple of the amethyst varies from 
the palest tints to the full rich velvety grape- 
purple of the so-called Siberian amethysts. 
The latter are of a reddish purple (sometimes 
almost red) by artificial light, but of a fine vio- 
let by daylight. No other purple stone ap- 



Color 95 

proaches them in fineness of coloring, so that 
here we have a real distinction based on color 
alone. If the purple is paler, however, one 
cannot be sure of the mineral by its color. Pur- 
ple corundum (Oriental amethyst) is seldom 
as fine in color as ordinary amethyst, and 
neves as fine as the best amethyst. It is usually 
of a redder purple,^and by artificial light is almost 
ruby-like in its color. 

Purple spinels are singly refracting, and lack 
dichroism, and hence lack variety of color. 
Almandine garnets also show no dichroism 
and lack variety of color. The garnets are, 
as a rule, apt to be more dense in color than 
the spinels. 

Purple spodumene (kunzite) is pinkish to 
lilac in shade — usually pale, unless in large 
masses, and it shows very marked dichroism. 
A yellowish cast of color may be seen in certain 
directions in it also, which will aid in distin- 
guishing it from other purple stones. 

Brown Stones, (i) Diamond, (2) garnet, 



96 Precious Stones 

(3) tourmaline, and (4) zircon furnish the prin- 
cipal brown stones. 

Diamond, when brown, unless of a deep 
and pleasing color, is very undesirable, as 
it absorbs much light, and appears dirty 
by daylight and dark and sleepy by arti- 
ficial light. .When of a fine golden brown 
a diamond may have considerable value as 
a "fancy" stone. Such "golden fancies" 
can be distinguished from other brown 
stones (except perhaps brown zircons) by 
their adamantine luster, and their prismatic 
play or "fire." 

Brown garnet (hessonite or cinnamon stone) , 
sometimes wrongly called hyacinth in the trade, 
is of a deep reddish brown color. Usually the 
interior structure, as seen under a lens, is 
streaky, having a sort of mixed oil and water 
appearance. 

Brown tourmaline is sometimes very pleasing 
in color. It is deep in shade, less red than 
cinnamon stone, and with marked dichroism, 



Color 97 

which both brown diamond and brown garnet 
lack 

Brown zircon, while lacking dichroism, is 
frequently rich and pleasing in shade, and when 
well cut is very snappy, the luster being 
almost adamantine, the dispersion being large, 
and^the refractive index high. It is useless to 
deny that by the unaided eye one might be 
deceived into thinking that a fine brown zircon 
was a brown diamond. However, the large 
double refraction of the zircon easily dis- 
tinguishes it from diamond (use the sun- 
light-card method or look for the doubling 
of the edges of the rear facets as seen through 
the table). The relative softness (7K) also 
easily differentiates it from diamond. 

Colorless Stones. Few colorless stones other 
than diamond, white sapphire (chiefly scientific), 
and quartz are seen in the trade. Colorless 
true topaz is sometimes sold and artificially 
whitened zircon (jargoon) is also occasionally 
met with. Beryl of very light green tint 



98 Precious Stones 

or even entirely colorless may also be seen at 
times. 

Such colorless stones must of course be 
distinguished by properties other than color. 
They are mentioned here merely that the 
learner may be aware of what varieties of 
gem minerals occur in the colorless condition, 
and that all these minerals also occur with 
color in their more usual forms. This does not 
even except the diamond, which is rarely truly 
colorless. 



LESSON XV 

HOW TO TELL SCIENTIFIC STONES FROM NATURAL 

GEMS 

IT should be said first that the only true 
scientific or synthetic stones on the market 
are those having the composition and proper- 
ties of corundum, that is to say, the ruby and 
the several color varieties of sapphire, as blue, 
pink, yellow, and white. There is also a green- 
ish stone that appears reddish by artificial light, 
which is called scientific alexandrite but which 
has, however, the composition and properties 
of the corundum gems rather than those of 
true alexandrite. All so-called " scientific emer- 
alds" have proved to be either of paste of one 
sort or another, or else triplets having a top 
and a back of some inexpensive but hard stone 

of pale color, and a central slice of deep green 

99 



100 Precious Stones 

glass, the three pieces being cemented together 
so skillfully that the junctions frequently escape 
any but a very careful examination with a lens. 

All Scientific Stones Are Corundum Gems. 
Now the fact that all true scientific stones 
are corundum gems makes their determination 
fairly simple on the following basis: Among 
the considerable number of corundum gems 
of nature, whether ruby or sapphire of various 
colors, there is seldom found one that is entirely 
free from defects. Almost always, even in 
what are regarded as fine specimens, one will 
easily find with a glass, defects in the crystalli- 
zation. Moreover these defects are character- 
istic of the corundum gems. 

The scientific corundum gems, however, never 
have these specific defects. Hence the surest 
and simplest way of distinguishing between 
the two kinds of stones is to acquaint oneself 
with the typical defects of natural corundum 
gems, and then to look for such defects in any 
specimen of ruby or sapphire that is in question. 



Scientific Stones and Natural Gems loi 

While a description of some of the most 
common of the typical defects of rubies and 
sapphires is to follow, the jeweler, who may not 
yet be familiar with them by actual experience, 
owes it to himself and to his customers to 
acquaint himself at first hand with the natural 
defopts of such material, which he is always 
in a position to do through the courtesy of 
representatives of houses dealing in precious 
stones, if he himself does not carry such material 
in stock. 

Typical Defects of Natural Conmdmn Gems. 
Perhaps the most common of the defects of 
natural corundum gems is the peculiar ap- 
pearance known as "silk." This is best seen 
when a strong light is allowed to stream through 
the stone at right angles to the observer's 
line of sight. Sets of fine, straight, parallel 
lines will be seen, and these will frequently meet 
other sets of similar lines at an angle of 120 
degrees (like the angle at which the sides of a 
regular hexagon meet) or the lines may cross 



I02 Precious Stones 

each other at that angle or at an angle of 60 
degrees (the supplement of 120 degrees). Such 
straight parallel lines are never seen in scientific 
stones, and their presence may be taken to 
indicate positively that the stone having them 
is a natural stone. In fine specimens of natural 
ruby or sapphire such lines will be few and 
difficult to find, but in some position or other 
they will usually be found if the search is even 
as careful as that which one would habitually 
employ in looking for defects in a diamond. 
In the vast majority of cases no such careful 
search will be required to locate "silk" in 
natural rubies, and if a stone that is apparently 
a ruby is free from such defects it is almost a 
foregone conclusion it is a scientific stone. 

Another common type of defect in corun- 
dum gems is the occurrence of patches of 
milky cloudiness within the material. A little 
actual acquaintance with the appearance of 
this sort of defect in natural stones will make 
it easy to distinguish from the occasional 



Scientific Stones and Natural Gems 103 

cloudiness found in scientific stones, which 
latter cloudiness is due to the presence of swarms 
of minute gas bubbles. These tiny bubbles 
can be seen under a high power lens, and this 
suggests a third feature that may be used to 
tell whether one has a natural stone or not. 

Natural rubies and sapphires, like scien- 
tific ones, frequently contain bubbles, but 
these are always angular in the natural stones, 
while those of the scientific stones are generally 
round or rounding, never angular. 

To sum up the suggestions already pre- 
sented it may be said that, since natural and 
scientific corundum gems are composed of 
essentially the same material, and have identi- 
cally the same physical and chemical properties, 
and frequently very closely resemble each other 
in color, it is necessary to have recourse to some 
other means of distinguishing between them. 
The best and simplest means for those who are 
acquainted with the structural defects common 
to natural corundum gems is to seek for such 



104 Precious Stones 

defects in any specimen that is in question, and 
if no such defects can be found, to be very 
sceptical as to the naturalness of the speci- 
men, inasmuch as perfect corundum gems 
are very rare in nature, and when of fine color 
command exceedingly high prices. No jeweler 
can afford to risk his reputation for knowledge 
and for integrity by selling as a natural stone 
any gem which does not possess the minor 
defects common to practically all corundum 
gems. 

Structural Defects of Scientific Stones. So 
far our tests have been mostly negative. It 
was said, however, that spherical bubbles some- 
times appear in scientific gems. Another char- 
acteristic structural defect of practically every 
scientific gem may be utilized to distinguish 
them. As is well known, the rough material is 
formed in boules or pear-shaped drops under 
an inverted blowpipe. The powdered material 
is fed in with one of the gases and passes through 
the flame, melting as it goes, and then accumu- 



Scientific Stones and Natural Gems 105 

lating and crystallizing below as a boule. The 
top or head of this boule is rounding from 
the start, and hence the successive layers of 
material gather in thin curved zones. The color 
and structure of these successive zones are not 
perfectly uniform, hence when cut stones are 
made from the boules these curving parallel 
layers may be seen within by the use of a good 
lens, especially if the cut stone is held in a 
strong crossing light, as was suggested when 
directions were given above as to the best way 
to look for " silk " in a natural stone. 

Owing to the shape of a well cut stone it 
is sometimes difficult to get light through the 
material, yet by turning the stone repeatedly, 
some position will be found in which the curving 
parallel striae can be seen. They are easily 
seen in scientific ruby, less easily in dark blue 
sapphire, but still they can be found on close 
search. In the light colored stones and in white 
sapphire, the difficulty is greater, as there 
are no color variations in the latter case. How- 



io6 Precious Stones 

ever, the value of white sapphire is so sHght, 
whether natural or artificial, that it is a matter 
of but little moment, and what has already, 
been said as to natural defects, applies to white 
sapphire as well as to the colored varieties, and 
absolutely clear and perfect natural white 
sapphire is rare. 

One more distinguishing mark of the scientific 
stones may be added to give full measure to 
the scheme of separation, that no one need be 
deceived. 

The surface finish of the scientific stones 
is rarely as good as that of the natural material 
and it appears to be more difficult to produce 
a good polish on scientific stones than on 
natural ones. The degree of hardness of the 
scientific stones seems to be slightly variable 
in different parts of the same piece so that the 
polishing material removes the surface material 
unequally, leaving minute streaky marks on 
the surfaces of the facets. Possibly this 
condition might be remedied by skillful treat- 



Scientific Stones and Natural Gems 107 

ment, but hardly at the price obtainable for the 
product, so that a close study of the surface 
finish will sometimes help in distinguishing 
between natural and artificial material. Any 
fine specimen of natural ruby or sapphire will 
have usually received very expert treatment and 
a splendid surface finish. 

In conclusion, then, the points to be re- 
membered in determining the origin of 
corundum gems are four in number. 

1. Expect to find natural defects, such 
as "silk" or cloudy patches, or angular bubbles 
in all natural stones. 

2. If bubbles are present in artificial 
material they will be round or rounding. 

3. Artificial material will always have 
curving parallel striae within it. 

4. The surface finish of artificial material 
is seldom or never equal to that of natural 
material. 

It ought not to be necessary to add that 
material from either source may be cut to 



io8 Precious Stones 

any shape, and that artificial rubies may- 
be seen in most Oriental garb, hence all speci- 
mens should have applied to them the above 
tests regardless of the seeming antiquity of their 
cut or of their alleged pedigree. 



LESSON XVI 

HOW TO TEST AN " UNKNOWN" GEM 

TJAVING now considered separately the 
principal physical properties by means 
of which one can identify a precious stone, 
let us attempt to give as good an idea as the 
printed page can convey of how one should go 
about determining to what species a gem be- 
longs. 

Signs of Wear in an Emerald. To make the 
matter more concrete, and therefore more 
interesting, let us consider a real case, the most 
recent problem, in fact, that the author has had 
to solve. A lady of some wealth had purchased, 
for a large sum, a green stone which purported 
to be an emerald. After a few years of wear as 
a ring stone she noticed one day that the 

stone had dulled around the edges of its table, 
109 



no Precious Stones 

and thinking that that ought not to be the 
case with a real emerald, she appealed to a 
dealer in diamonds to know if her stone was a 
real emerald. The diamond merchant told 
her frankly that, while he was competent in all 
matters pertaining to diamonds, he could not 
be sure of himself regarding colored stones, 
and advised the lady to see the author. 

The matter being thus introduced, the lady 
was at once informed that even a real emer- 
ald might show signs of wear after a few years 
of the hard use that comes to a ring stone. 

While emerald has, as we saw in the lesson on 
hardness, a degree of hardness rated as nearly 
8 (7>2 in the table), it is nevertheless a rather 
brittle material and the long series of tiny blows 
that a ring stone is bound to meet with will cause 
minute yielding along the exposed edges and 
corners of the top facets. This being an- 
nounced, the first step in the examination of 
the stone was to clean it and to give it a 
careful examination with a ten-power lens. (An 



To Test an "Unknown" Gem iii 

aplanatic triplet will be found best for this 
purpose.) 

Color. The color was, of course, the most 
obvious property, but, as has already been said, 
color is not to be relied upon in all cases. In 
this case the color was a good emerald green but 
a bit i)luer than the finest grass green. A very 
fine Maine tourmaline might approach this 
stone in color, so it became necessary to consider 
this possibility. A glass imitation, too, might 
have a color equal or superior to this. 

Imperfections. While noting the color, the 
imperfections of the stone claimed attention. 
They consisted mainly of minute jagged cracks 
of the character peculiar to brittle materials 
such as both emerald and tourmaline. So 
far it will be noted either of the above minerals 
might have furnished the lady's gem. As glass 
can be artificially crackled to produce similar 
flaws the stone might have been only an imi- 
tation as far as anything yet learned about it 
goes. 



112 Precious Stones 

File Test. The next step was to test its 
hardness by gently applying a very fine file to 
an exposed point at one corner of the girdle. 
The file slipped on the material as a skate 
slips on ice. Evidently we did not have to 
do with a glass imitation. 

Refraction. Knowing now that we hadi a 
true hard mineral, it remained to be determined 
what mineral it was. On holding the stone in 
direct sunlight and reflecting the light onto a 
white card' it was seen at once that the mate- 
rial was doubly refracting, for a series of 
double images of the back facets appeared. 
These double images might have been produced 
by tourmaline as well as by emerald. (Not how- 
ever by glass which is singly refracting.) If a 
direct reading refractometer had been available 
the matter could have been settled at once 
by reading the refractive indices of the material, 
for tourmaline and emerald have not only 
different refractive indices but have double 
refraction to different degrees. Such an instru- 



To Test an ** Unknown" Gem 113 

ment was not available at the time and will 
hardly be available to most of those who are 
studying this lesson, so we can go on with our 
account of the further testing of the green stone. 

Hardness. A test upon the surface of a 
quartz crystal showed that the stone was harder 
than, quartz (but so is tourmaline). A true 
topaz crystal was too hard for the ring stone, 
whose edge slipped over the smooth topaz 
surface. The green stone was therefore not a 
green corundum (Oriental emerald) as the latter 
has hardness 9 and scratches topaz. 

With hardness evidently between 7 and 
8 and with double refraction and with the kind 
of flaws peculiar to rather brittle minerals we 
had in all probability either a tourmaline or 
an emerald. 

Dichroism. The dichroscope (which might 
have been used much earlier in the test but was 
not at hand at the time) was next tried and 
the stone was seen to have marked dichro- 
ism — a bluish green and a yellowish green 



114 Precious Stones 

appearing in the two squares of the instru- 
ment when the stone was held in front of the 
opening and viewed against a strong light. 

As either tourmaline or emerald might 
thus exhibit dichroism (the tourmaline more 
strongly, however, than the emerald) one more 
test was tried to finally decide the matter. 

Specific Gravity. The stone was removed 
from its setting and two specific gravity deter- 
minations made by means of a specific gravity 
bottle and a fine chemical balance. The 
two results, which came closely alike, aver- 
aged 2.70 which agrees very nearly with emer- 
ald (2.74) and which is far removed from 
the specific gravity of tourmaline (3.10). 
The stone was now definitely known to 
be an emerald, as each of several tests agreed 
with the properties of emerald, namely : 

Color — nearly grass green. 

Imperfections — like those of emerald. 

Hardness — 7^. 

Refraction — double. 



To Test an ''Unknown" Gem 115 

Dichroism — easily noted. 
Specific gravity — 2.70. 

While one who was accustomed to deal 
in fine emeralds might not need to make as 
detailed an examination of the stone as has just 
been indicated above, yet for most of us who 
do ttot have many opportunities of studying 
valuable emeralds it is safer to make sure by 
complete tests. 

One other concrete example of how to go 
about testing unknown stones must suffice 
to' conclude this lesson, after which the student, 
who has mastered the separate lessons preced- 
ing this, should proceed to test as many "un- 
knowns" as his time and industry permit in 
order to really make his own the matter of these 
lessons. It may be added here that the task 
of testing a stone is much more rapid than this 
laborious effort to teach others how to do it 
might indicate. To one skilled in these matters 
only a few seconds are required for the inspection 
of a stone with the lens, the dichroscope, or the 



ii6 Precious Stones 

refractometer, and hardness tests are swiftly- 
made. A specific gravity test requires more 
time and should be resorted to only when there 
remains a reasonable doubt after other tests 
have been applied. 

Now for oiu" final example. A red stone, 
cut in the form of a pear shaped brilliant, 
was submitted to the writer for determina- 
tion. It had been acquired by an Ameri- 
can gentleman in Japan from an East Indian 
who was in financial straits. Along with it, 
as security for a loan, the American obtained a 
number of smaller red stones, a bluish stone, and 
a larger red stone. The red stones were all 
supposed to be rubies. On examination of 
the larger red stone with a lens it was at once 
noted that the internal structure was that of 
scientific ruby. 

Testing Other Stones. Somewhat dashed by 
the announcement of this discovery the owner 
began to fear that all his gems were false. 
Examination of the small red stones showed 



To Test an ** Unknown" Gem 117 

abundance of "silk, " a peculiar fibrous appear- 
ance within the stone caused by its internal 
structure. The fibers were straight and parallel, 
not curved and parallel as in synthetic ruby. 
Tiny bubbles of angular shape also indicated 
that the small stones were natural rubies. 
They exhibited dichroism and scratched topaz 
and it was therefore decided that they at 
least were genuine. 

The pear shaped brilliant which was first 
mentioned was of a peculiar, slightly yellowish, 
red color. It was very pellucid and free from 
any stri^ either of the straight or curved types. 
It had in fact no flaws except a rather large nick 
on one of the back surfaces near the girdle. 
This was not in evidence from the front of the 
stone and had evidently been left by the 
Oriental gem cutter to avoid loss in weight 
while cutting the stone. 

The peculiar yellowish character of the 
red color led us to suspect ruby spinel. The 
stone was therefore inspected with the dichro- 



ii8 Precious Stones 

scope and found to possess no dichroism. 
The sunlight-card test, too, showed that the 
stone was singly refracting. 

A test of the hardness showed that the 
material barely scratched topaz, but was 
attacked by sapphire. It was therefore judged 
to be a red spinel. 

The large bluish stone which the gentleman 
acquired with the red stones proved to be 
iolite, sometimes called cordierite or water- 
sapphire {Saphire d'eau), a stone seldom seen 
in this country. It had marked dichroism — 
showing a smoky blue color in one direction and 
a yellowish white in another. The difference 
was so marked as to be easily seen without the 
dichroscope. 



LESSON XVII 

SUITABILITY OF STONES FOR VARIOUS TYPES OF 

JEWELS AS DETERMINED BY HARDNESS, 

BRITTLENESS, AND CLEAVABILITY 

Hard Stones not Necessarily Tough. As 

was suggested in the lesson on hardness there 
is prevalent in the public mind an erron- 
eous belief that hardness carries with it ability 
to resist blows as well as abrasion. Now that 
it does not follow that because a precious stone is 
very hard, it will wear well, should be made plain. 
Some rather hard minerals are seldom or 
never used as gems, in spite of considerable 
beauty and hardness, because of their great 
brittleness. Other stones, while fairly hard 
and reasonably tough in certain directions, 
have nevertheless so pronounced a cleavage 
that they do not wear well if cut, and are 

sometimes very difficult to cut at all. 
119 



120 Precious Stones 

In view of these facts it will be well to con- 
sider briefly what stones, among those most in 
use, are sufficiently tough as well as hard, 
to give good service in jewels, such as rings, 
which are subject to rough wear. We may 
also consider those stones, whose softness, or 
brittleness, or ready cleavability, requires that 
they should be reserved for use only in those 
jewels which, because of their nature, receive less 
rough usage. 

In order to deal with the principal gems 
systematically, let us consider them in the 
order of their hardness, beginning with the 
hardest gem material known, which is, of 
course, diamond. 

Durability of the Diamond. Fortunately 
this king of gems possesses in addition to its 
great hardness, considerable toughness, and 
although it is readily cleavable in certain direc- 
tions it nevertheless requires a notable amount 
of force applied in a particular direction to 
cause it to cleave. Although sharp knocks will 



Hardness, Brittleness, Cleavability 121 

occasionally flake off thin layers from diamonds 
when roughly worn in rings, or even in extreme 
cases fracture them, yet this happens but seldom 
and, as the enormous use of the diamond in ring 
mountings proves, it is entirely suitable for that 
purpose. It follows that, if a stone can stand 
ring_,usage, it can safely be used for any purpose 
for which precious stones are mounted. 

The Corundum Gems. Next after the dia- 
mond in hardness come the corundum gems, i. e., 
ruby, sapphire, and the series of corundum gems 
of colors other than red and blue. These 
stones have no noticeable cleavage and are 
exceedingly tough, for minerals, as well as 
very hard. We have only to consider the 
use of impure corundum (emery) as a commer- 
cial abrasive in emery wheels, emery cloth, 
emery paper, etc., to see that the material is 
tough. Any of the corundum gems therefore 
may be used in any type of jewel without 
undue risk of wear or breakage. Customers of 
jewelers should, however, be cautioned against 



122 Precious Stones 

wearing ruby or sapphire rings on the same 
finger with a diamond ring in cases where it 
would be possible for the two stones to rub 
against each other. So much harder than 
the ruby is the diamond (in spite of the seem- 
ing closeness of position in Mohs's scale) that 
the slightest touch upon a ruby surface with a 
diamond will produce a pronounced scratch. 
The possessor of diamonds and other stones 
should also be cautioned against keeping them 
loose in the same jewel case or other container, as 
the shaking together may result in the scratch- 
ing of the softer materials. The Arabs are 
said to have a legend to the effect that the 
diamond is an angry stone and that it should 
not be allowed to associate with other stones 
lest it scratch them. 

Chrysoberyl. Passing on to the next mineral 
in the scale of hardness we come to chrysoberyl, 
which is rated as 8>^ on Mohs's scale. This 
mineral furnishes us the gem, alexandrite, 
which is notable for its power to change in 



Hardness, Brittleness, Cleavability 123 

color from green in daylight to red in arti- 
ficial light. Chrysoberyl also supplies the 
finest cat's-eyes (when the material is of a sufli- 
ciently fibrous or tubular structure), and it 
further supplies the greenish yellow stones 
frequently (though incorrectly) called " chryso- 
lite • by jewelers. The material is very hard 
and reasonably tough and may be used in almost 
any suitable mounting. 

Spinel. After chrysoberyl come the materials 
rated as about 8 in hardness. First and 
hardest of these is spinel, then comes true 
or precious topaz. The various spinels are 
very hard and tough stones. The rough 
material persists in turbulent mountain streams 
where weaker minerals are ground to powder, 
and when cut and polished, spinel will wear 
well in any jewel. The author has long worn a 
rub}'' spinel in a ring on the right hand and has 
done many things that have subjected it to hard 
knocks, yet it is still intact, except for a spot 
that accidentally came in contact with a fast- 



124 Precious Stones 

flying carborundiim wheel, which of course 
abraded the spinel. 

Topaz. The true topaz is a bit softer than 
spinel, and the rough crystals show a very per- 
fect basal cleavage. That is, they will cleave 
in a plane parallel to the bases of the usual 
orthorhombic crystals. This being the case 
a cut topaz is very likely to be damaged by 
a blow or even by being dropped on a hard 
surface, and it would be wiser not to set such a 
stone in a ring unless it was to be but little 
used, or used by one who would not engage 
in rough work while wearing it. Thus a lady 
might wear a topaz ring on dress occasions for a 
long time without damaging it, but it would not 
do for a machinist to wear one in a ring. 

Gems between 7 and 8 in Hardness. We 
now come to a rather long list of gem minerals 
ranging between 7 and 8 in hardness. Of these 
the principal ones are zircon, almandine garnet, 
and beryl (emerald and aquamarine) rated as 
7>2 in hardness, and pyrope and hessonite 



Hardness, Brittleness, Cleavability 125 

garnet rated as 7>^ in hardness. Tourmaline 
and kunzite may also be included in. this group 
as being on the average slightly above 7 in 
hardness. 

The above minerals are all harder than 
quartz, and hence not subject to abrasion 
by t^e quartz dust which is everywhere present. 
In this respect they are suitable for fairly hard 
wear. The garnets are of sufficient tough- 
ness so that they may be freely used in rings — 
and the extensive use of thin slices of garnet 
to top doublets proves the suitability of the 
material for resisting wear. The zircon is 
rather more brittle and the artificially whitened 
zircons (known as jargoons) are especially sub- 
ject to breakage when worn in rings. For- 
tunately jargoons are not commonly sold. 

The beryl, whether emerald or aquamarine, 
is rather brittle. Emeralds are seldom found in 
river gravels. The material cannot persist in 
the mountain streams that bring down other 
and tougher minerals. The extreme beauty and 



126 Precious Stones 

value of the emerald has led to its use in the 
finest jewels, and the temptation is strong to set 
it in rings, especially in rings for ladies. If such 
rings are worn with the care that valuable jewels 
should receive they will probably last a long time 
without any more serious damage than the 
dulling of the sharp edges of the facets around 
the table. This slight damage can at any time 
be repaired by a light repolishing of the affected 
facets. If an emerald is already badly shat- 
tered, or as it is called "mossy" in character, 
it will not be wise to set it in a ring, as a slight 
shock might complete its fracture. What 
has been said about emerald applies equally 
to aquamarine except that the value at stake 
is much less and the material is usually much 
freer from cracks. 

Tourmalines, like emeralds, are brittle, and 
should be treated accordingly. Here, however, 
we are dealing with a much less expensive mate- 
rial than emerald, and if a customer desires a 
tourmaline in a ring mounting, while it will be 



Hardness, Brittleness, Cleavability 127 

best to suggest care in wearing it, the loss, in 
case of breakage, will usually be slight. 

Kunzite, like all spodumene, has a pro- 
nounced cleavage. It should therefore be 
used in brooches, pendants, and such jewels, 
rather than in rings. Lapidaries dislike to 
cut it under some conditions because of its 
fragility. 

Quartz Gems. Coming down to hardness 7 
we have the various quartz gems and jade (vari- 
ety jadeite). The principal quartz gems are, of 
course, amethyst and citrine quartz (the stone 
that is almost universally called topaz in the 
trade). As crystalline quartz is fairly tough"and 
lacks any pronounced cleavage, and as it is as 
hard as anything it is likely to meet with in use, 
it is a durable stone in rings or in other mount- 
ings. In the course of time the sharp edges will 
wear dull from friction with objects carrying 
common dust, which is largely composed of pow- 
dered quartz itself, and which therefore gradu- 
ally dulls a quartz gem. Old amethysts or 



128 Precious Stones 

"topazes" that have been long in use in rings 
show this dulUng. There is, however, Httle 
danger of fracture with amethyst or "topaz" 
unless the blow is severe and then any stone 
might yield. 

The many semi-precious stones which have 
a quartz basis (such as the varieties of waxy 
or cryptocrystalline chalcedony which is largely 
quartz in a very minutely crystalline condition) 
are often even tougher than the clear crystal- 
lized quartz. Carnelian, agate, quartz cat's-eye, 
jasper (containing earthy impurities), and those 
materials in which quartz has more or less 
completely replaced other substances, such as 
silicified crocidolite, petrified wood, chrysocoUa, 
quartz, etc., are all nearly as hard and quite as 
tough as quartz itself, and they make admirable 
stones for inexpensive rings of the arts and 
crafts type. 

Jade. Jade, of the jadeite variety, which is 
rarer than the nephrite jade, and more highly 
regarded by the Chinese, is an exceedingly tough 



Hardness, Brittleness, Cleavability 129 

material. One can beat a chunk of the rough 
material with a hammer without making much 
impression upon it. It is also fairiy hard, 
about as hard as quartz, and with the two 
properties of toughness and hardness it possesses 
excellent wearing qualities in any kind of 
mounting. True jade, whether jadeite or 
nephrite, deserves a larger use in inexpensive 
ornaments, as it may be had of very fine green 
color and it is inexpensive and durable. 

Softer Stones. Coming next to those min- 
erals whose hardness is 6 or over, but less than 
7, we have to consider jade of the nephrite 
variety, demantoid garnet ("olivine" of the 
trade), peridot (or chrysolite, or the olivine of 
the mineralogist), turquoise, moonstone, and 
opal. 

As has already been said of jadeite, the 
jade of the nephrite variety, while slightly 
less hard, is about as tough a mineral as one 
could expect to find. It can take care of itself 
in any situation. 



I30 Precious Stones 

The demantoid garnet (the "olivine" of 
the trade) is so beautiful and brilliant a stone 
that it is a pity that it is so lacking in hardness. 
It will do very well for mounting in such jewels 
as scarf pins, lavallieres, etc., where but little 
hard wear is met with, but it cannot be recom • 
mended for hard ring use. 

The peridot, too, is rather soft for ring use 
and will last much better in scarf pins or other 
mountings little subject to rubbing or to shocks. 

Turquoise, although rather soft, is fairly 
tough, as its waxy luster might make one 
suppose, and in addition, being an opaque 
stone, slight dulling or scratching hardly 
lessens its beauty. It may therefore be used 
in ring mountings. However, it should be 
suggested that most turquoise is sufficiently 
porous to absorb grease, oil, or other liquids, 
and its color is frequently ruined thereby. Of 
course, such a change is far more likely to occur 
to a ring stone than to a turquoise mounted 
in some more protected situation. 



Hardness, Brittleness, Cleavability 131 

The moonstone, being a variety of feldspar, 
has the pronounced cleavage of that mineral 
and will not stand blows without exhibiting 
this property. Moonstones are therefore better 
suited to the less rude service in brooch mount- 
ings, etc., than to that of ring stones. How- 
ever^ being comparatively inexpensive, many 
moonstones, especially of the choicer bluish 
type, are set in ring mountings. The lack of 
hardness may be expected to dull their surfaces 
in time even though no shock starts a cleavage. 

The Opal. There remains the opal, of hard- 
ness 6, to be considered. As is well known opal 
is a solidified jelly of siliceous composition, 
containing also combined water. It is not 
only soft but very brittle and it will crack 
very easily. Many opals crack in the paper 
in which they are sold, perhaps because of 
unequal expansion or contraction, due to heat or 
cold. In spite of this fragility, thousands of 
fine opals, and a host of commoner ones, are set 
in rings, where many of them subsequently 



132 Precious Stones 

come to a violent end, and all, sooner or later, 
become dulled and require repolishing. 

The great beauty of the opal, rivaling any 
mineral in its color-play, causes us to chance 
the risk of damage in order to mount it where 
its vivid hues may be advantageously viewed 
by the wearer as well as by others. 

Very Soft Stones. Of stones softer than 6 we 
have but few and none of them is really fit for 
hard service. Lapis lazuli, 5^/2 in hardness, has 
a beautiful blue color, frequently flecked with 
white or with bits of fool's gold. Its surface 
soon becomes dulled by hard wear. 

Two more of the softer materials, malachite 
and azurite, remain to be described. These 
are both varieties of copper carbonate with 
combined water, the azurite having less water. 
Both take a good polish, but fail to retain it in 
use, being only of hardness 3>^ to 4. 



LESSON XVIII 

MINERAL SPECIES TO WHICH THE VARIOUS GEMS 
BELONG AND THE CHEMICAL COM- 
POSITION THEREOF 

A LTHOUGH we have a very large number 
of different kinds of precious and semi- 
precious stones, to judge by the long list 
of names to be found in books on gems, yet all 
these stones can be rather simply classified on 
the basis of their chemical composition, into 
one or another of a comparatively small number 
of mineral species. While jewelers seldom 
make use of a knowledge of the chemistry of the 
precious stones in identifying them, nevertheless 
such a knowledge is useful, both by way of 
information, and because it leads to a bet- 
ter and clearer understanding of the many 
similarities among stones whose color might 

lead one to regard them as dissimilar. 
133 



134 Precious Stones 

Mineral Species. We must first consider 
what is meant by a "mineral species" and find 
out what relation exists between that subject 
and chemical composition. Now by a "mineral 
species" is understood a single substance, 
having (except for mechanically admixed 
impurities) practically a constant chemical 
composition, and having practically identical 
physical properties in all specimens of it. 

Diamond and Corundum. A chemist would 
call a true mineral a pure substance, just as sugar 
and salt are pure substances to the chemist. 
Thus diamond is a "mineral species, " as is also 
corundum. There are many different colors 
of both diamond and corundum, but these 
different colors are believed to be due to the 
presence in the pure substance of impurities in 
small amounts. Thus every diamond consists 
mainly of pure carbon, and all the corundum 
gems {ruby and the various colors of sapphire) 
consist mainly of pure oxide of aluminum. The 
properties of all diamonds are practically alike 



Their Chemical Composition 135 

and so are the properties of all the corun- 
dum gems whether red (ruby), blue (sap- 
phire), yellow (Oriental topaz), green (Oriental 
emerald), or purple (Oriental amethyst). 

Thus all diamonds, of whatever, color be- 
long to the one species, diamond, and in this 
case*the usual custom in naming them agrees 
with the facts. Similarly all sapphires, of 
whatever color, belong to the mineral species 
"corundum, " Thus a ruby is a red corundum. 

The old French traveler and gem merchant, 
Tavernier, tells us that in the seventeenth cen- 
tury, when he visited the mines of Pegu, the na- 
tives knew of the similarity of the corundum 
gems and even called all by one name, with other 
names attached to designate the color. Singu- 
larly enough, the common name used by them 
was ruby rather than sapphire, as now. Thus 
they called blue corundum gems blue rubies; 
yellow corundums, yellow rubies, etc. 

It is easily seen that if one recognizes the 
similar nature of all the many colors and shades 



136 Precious Stones 

of corundum that the number of things that one 
has to remember in order to be well acquainted 
with these stones is considerably diminished. 
Thus, instead of having a whole series of specific 
gravities to remember one has only to remem- 
ber that all the corundum gems have a speci- 
fic gravity of approximately 4. Similarly they 
are all of practically the same refractive in- 
dex (1.761-1. 770, being doubly refracting) that 
they all exhibit dichroism when at all deeply 
colored, etc. 

Having thus indicated what we mean by 
mineral species and having illustrated the 
matter by the cases of diamond and corun- 
dum and further having stated that all dia- 
monds are composed of pure carbon (except 
for traces of impurities) and all corundum gems 
mainly of oxide of aluminum, we may proceed 
to consider other mineral species and find out 
what gems they afford us. 

Carbon, the only Element Furnishing a Gem. 
It will be noted that the first species con- 



Their Chemical Composition 137 

sidered, diamond, consisted of but a single 
element, carbon. It is thus exceedingly simple 
in composition, being not only a pure substance 
but, in addition, an elementary substance. 
Corundum, the second species considered, was 
a little more complex, having two elements, 
alunainum and oxygen, in its make-up, but 
completely and definitely combined in a new 
compound that resembles neither aluminum nor 
oxygen. It is thus a compound substance. 
No other element than carbon affords any 
gem-stone when by itself. 

Oxides of Metals. There is, however, an- 
other oxide, in addition to aluminum oxide, 
that furnishes gem material. It is silicon oxide, 
containing the two elements silicon and oxygen. 
Silicon itself is a dark, gray, crystalline ele- 
ment that seems half metallic, half non-metallic 
in its properties. It is never found by itself 
in nature but about twenty-eight per cent, of 
the crust of the earth is composed of it in com- 
pound forms, and one of the most abundant of 



138 Precious Stones 

these is quartz, which is a mineral species, and 
which contains just silicon and oxygen. That 
is, it is oxide of silicon. Now quartz is colorless 
when pure {rock crystal), but it is frequently 
found colored purple (probably by oxide of 
manganese) and it is then called amethyst 
by the jeweler. At other times its color is 
yellow (due to oxide of iron) and then the 
jeweler is prone to call it "topaz,'" although 
properly speaking that name should, as we shall 
soon see, be reserved for an entirely different 
mineral species. Chalcedony too (which when 
banded furnishes us our agates, and when red- 
dish our carnelian) is a variety of quartz, and 
prase is only quartz colored green by fibers of 
actinolite within it. 

The common cat's-eye and the tiger'' s-eye are 
varieties of quartz enclosing fibrous minerals or 
replacing them while still keeping the arrange- 
ment that they had. ''Venus hair stone*' is 
quartz containing needle-like crystals of rutile, 
and "iris" is quartz that has been crackled 



Their Chemical Composition 139 

within, so as to produce rainbow colors, because 
of the effects of thin layers of material. Aven- 
turine quartz (sometimes called goldstone) has 
spangles of mica or of some other mineral 
enclosed in it. The, jaspers are mainly quartz 
with more of earthy impurity than the preced- 
ing g;tones. 

Thus all this long list of stones of differ- 
ing names can be classified under the one 
mineral species, quartz. Together they consti- 
tute the quartz gems. In properties they are 
essentially alike, having specific gravity 2.66, 
hardness 7, slight double refraction, etc., the 
slight differences that exist being due only to the 
presence of varying amounts of foreign matter. 

Opal. The opal may be considered along 
with the quartz gems, because, like them, it 
is composed mainly of oxide of silicon, but 
the opal also has water combined with the 
silicon oxide (not merely imprisoned in it). 
Thus opal is a hydrous form of silica (hydrous 
comes from the Greek word for water). 



140 Precious Stones 

Spinel. All our other stones are of more com- 
plicated chemical composition than the preced- 
ing. Coming now to mineral species which 
have three chemical elements in them we may 
consider first spinel, which has the two metallic 
elements aluminum and magnesium and the 
non-metallic element oxygen in it. It is 
virtually a compound of the two oxides, alumin- 
um oxide and magnesium oxide. The variously 
colored spinels, like the various corundums, 
all have the same properties, thus they are 
all of hardness 8 or a little higher, they all 
have single refraction, and all have specific 
gravity 3.60. 

Chrysoberyl. Another mineral species which, 
like spinel, has just three elements in its com- 
position is chrysoberyl. This mineral con- 
tains the metals aluminum and berylium 
combined with the non-metal oxygen. Thus 
it is really to be regarded as a compound of the 
two oxides, aluminum oxide and berylium oxide. 
This species furnishes us Alexandrite, chrysoberyl 



Their Chemical Composition 141 

cat^s-eye and less valuable chrysoberyls of yel- 
lowish green color. All are of the one species, 
the marked color difference being due to the 
presence of different impurities. The cat's- 
eye effect in one of the varieties is due to the 
internal structure rather than to the nature of 
the material. 

The Silicates. Nearly all of the remaining 
precious stones belong to a great group of 
mineral species known as the silicates. These 
are so called because they consist largely of 
oxide of silicon (the material above referred to 
under quartz gems) . This oxide of silicon is not 
free and separate in the silicates but is com- 
bined chemically with other oxides, chiefly with 
metallic oxides. Thus there are many different 
silicates because, in the earth, many different 
metallic oxides have combined with silicon 
oxide. Also in many cases two or three or 
even more metallic oxides have combined with 
silicon oxide to make single new compounds. 

Glass a Mixture of Silicates. Those who are 



142 Precious Stones 

familiar with glass making may receive some 
help at this point by remembering that the 
various glasses are silicates, for they are made 
by melting sand (which is nearly pure oxide of 
silicon) with various metallic oxides. With 
lime (calcium oxide) and soda (which yields 
sodium oxide) we get soda-lime glass (common 
window glass). Lead oxide being added to the 
mixture a dense, very brilliant, but soft glass 
(flint glass) results. Cut glass dishes and 
' ' paste ' ' gems are made of this flint glass. Now 
the glasses, although they are silicates, are not 
crystalline, but rather they are amorphous, 
that is, without any definite structure. Na- 
ture's silicates, on the other hand, are usually 
crystallized or at least crystalline in structure. 
(In a few cases we find true glasses, volcanic 
glass, or obsidian, for example.) 

Having thus introduced the silicates we 
may now consider which ones among the 
many mineral silicates furnish us with precious 
or semi-precious stones. 



Their Chemical Composition 143 

Beryl, Emerald, and Aquamarine. First in 
value among the silicates is heryl, which, when 
grass green, we call emerald. The aquamarine 
and golden beryl too belong to this same species. 
Beryl is a silicate of aluminum and berylium. 
That is, it is a compound in which oxide of 
silicon is united with the oxides of aluminum 
and of berylium. There are thus four chemical 
elements combined in the one substance and it 
is hence more complicated in its composition 
than any of the gems that we have yet consid- 
ered. It is worthy of note that aluminum 
occurs in the majority of precious stones, the 
only species so far considered that lack it being 
diamond, and the quartz gems. 

Perhaps the silicates that are next in impor- 
tance to the jeweler, after beryl, are those 
which form the garnets of various types. There 
are four principal varieties of garnet (although 
specimens of garnet frequently show a crossing 
or blending of the types). 

Garnets. The types are (i) Almandite gar- 



144 Precious Stones 

net; (2) Pyrope garnet; (3) Hessonite garnet; 
and (4) Andradite garnet. These are all 
silicates, the almandite garnets being silicates 
of iron and aluminum; the pyrope garnets are 
silicates of magnesium and aluminum; the 
hessonite garnets, silicates of calcium and 
aluminum, and the andradite garnets, silicates 
of calcium and iron. 

The so-called almandine garnets of the 
jeweler are frequently of the almandite class 
and tend to purplish red. The pyrope garnets 
are, as the name literally implies, of fire red 
color, as a rule, but they also may be purplish 
in color. The hessonite garnets are frequently 
brownish red and are sometimes called "cinna- 
mon stones." The andradite garnets furnish 
the brilliant, nearly emerald green demantoids 
(so often called "olivine'' by the trade). 

Thus all the garnets are silicates and yet we 
have these four principal mineral species, which, 
however, are more closely related to each other 
in crystal form, in character of composition and 



Their Chemical Composition 145 

in general properties, than is usual among the 
other silicates. Specimens which have any 
one of the four types of composition unblended 
with any of the other types would be found to 
be exactly ahke in properties. As was sug- 
gested above, however, there is a great tend- 
ency to blend and this is well illustrated by the 
magnificent rhodolite garnets, of rhododendron 
hue which were found in Macon County, North 
Carolina. These had a composition between 
almandite and pyrope, that is, they had both 
magnesium and iion with aluminum and 
silica. 

The true topaz next calls for considera- 
tion as it too is a silicate. The metallic part 
consists of aluminum, and there are present 
also the non-metals fluorine and hydrogen. 
Here we have five elements in the one sub- 
stance. Various specimens of this species may 
be wine yellow, light blue, or bluish green, 
pink or colorless, yet they all have essentially 
the same properties. 



146 Precious Stones 

Toiirmaline is about as complicated a mineral 
as we have. It is a very complex silicate, 
containing aluminum, magnesium, sodium (or 
other alkali metal, as, for example, lithium), 
iron, boron, and hydrogen. As Ruskin says 
of it in his The Ethics of the Dust, when Mary 
asks "and what is it made of?" "A little of 
everything; there's always flint (silica) and clay 
(alumina) and magnesia in it and the black 
is iron, according to its fancy; and there's 
boracic acid, if you know what that is: and if 
you don't, I cannot tell you to-day and it 
doesn't signify; and there's potash and soda; 
and on the whole, the chemistry of it is more like 
a medieval doctor's prescription, than the mak- 
ing of a respectable mineral. " The various 
tourmalines very closely resemble each other 
in their properties, the slight differences cor- 
responding to differences in composition do not 
alter the general nature of the material. 

Moonstone belongs to a species of min- 
eral known as feldspar. The particular feld- 



Their Chemical Composition 147 

spar that furnishes most of the moonstone is or- 
thoclase, a silicate of potassium and aluminum. 
Another feldspar sometimes seen as a semi- 
precious stone is Labradorite. Amazonite, also 
is a feldspar. Sunstone is a feldspar which 
includes tiny flakes or spangles of some other 
mineral. 

The mineral species olivine gives us peridot. 
It is a silicate of magnesium. 

Zircon is itself a species of mineral and 
is a silicate of zirconium. The names hya- 
cinth, jacinth, and jargoon are applied to 
red, yellow, and colorless zircon in the order 
as given. 

Jade may be of any of several different 
species of minerals, all of which are very tough. 
The principal jades belong, however, to one or 
the other of two species, jadeite and nephrite. 
Jadeite is a sodium aluminum silicate and 
nephrite, a calcium magnesium silicate. 

Leaving the silicates we find very few gem 
minerals remaining. The phosphates furnish 



148 Precious Stones 

us turquoise, a hydrous aluminum phosphate, 
with copper and iron. Varicite is also a phos- 
phate (a hydrated aluminum phosphate). 

The carbonates give us malachite and azurite, 
both carbonates of copper with combined 
water, the malachite having more water. 



LESSON XIX 

THE NAMING OF PRECIOUS STONES 

/^WING to the confusion which may re- 
^"'^ suit from a lack of uniformity in the nam- 
ing of precious stones, it is very desirable that 
jewelers and stone merchants inform them- 
selves in regard to the correct use of the names 
of the gems, and that they use care in speaking 
and in writing such names. 

As nearly all precious and semi-precious 
stones are derived from a relatively small 
number of mineral species, as we saw in Lesson 
XVIIL, and as the science of mineralogy has 
a very orderly and systematic method of naming 
the minerals, the best results are had in the nam- 
ing of gems when we use, as far as is possible, 
the language of mineralogy. 

Ancient Usage. Long established custom 
149 



150 Precious Stones 

and usage, however, must be observed, for any 
system of naming must be generally under- 
stood in order to be useful. Thus the proper 
name for blood red, crystallized oxide of alumi- 
num, of gem quality, according to the min- 
eralogical system of naming, would be red 
corundum, but that same material is referred 
to in the Old Testament thus (in speaking of 
wisdom), ''She is more precious than rubles.^' 
It is obviously necessary to keep and to use all 
such terms as have been for years established 
in usage, even though they do not agree with 
the scientific method of naming the particular 
mineral. It is, however, necessary that any 
name, thus retained, should be correctly used, 
and that it should not be applied to more than 
one material. Thus the term ruby should be 
reserved exclusively for red corundum, and not 
applied to other red minerals such as garnet, 
spinel, etc., as is too often done. 

It will be the purpose of this lesson to attempt 
to set forth as clearly and as briefly as possible 



Naming of Precious Stones 151 

what constitutes good usage in the naming 
of the principal stones, and also to point out 
what incorrect usage is most in need of being 
avoided. 

To cover the subject systematically we 
will adopt the order of hardness that we did 
in discussing mineral species in Lesson XVIII. 

Fancy Diamonds. Beginning with the hard- 
est of all gems, the diamond, we have no diffi- 
culty as regards naming, as all specimens of 
this mineral, regardless of color, are called dia- 
monds. When it is necessary to designate 
particular colors or tints, or differences in 
tint, additional names are used — for exam- 
ple, all diamonds of pronounced and pleas- 
ing color are called "fancy" diamonds in 
the trade. Certain of these "fancy" dia- 
monds are still further defined by using a 
name specifying the color, as, for example, 
"canary" diamonds (when of a fine bright 
yellow), or "golden fancies," when of a fine 
golden brown, or "orange," or "pink," or 



152 Precious Stones 

"absinthe green," or "violet," as the case 
may be. 

Names of Various Grades of White Dia- 
monds. The great majority of the diamonds 
which come on the market as cut stones belong, 
however, to the group which would be spoken of 
as white diamonds, but many qualifying names 
are needed to express the degree of approach to 
pure white possessed by different grades of these 
diamonds. Thus the terms : i , Jdgers; 2, Rivers; 
3, Blue Wesseltons; 4, Wesseltons; 5, Top Crys- 
tals; 6, Crystals; 7, very light brown; 8, Top 
Silver Capes; 9, Silver Capes; 10, Capes; 11, 
Yellows, and 12, Browns, describe increasing 
depth of color, and hence decreasing value in 
diamonds. 

Popular Names. Certain' more popular 
names for diamonds of differing degrees of 
whiteness may next be set forth. The term 
"blue white" (a much abused expression, by 
the way) should be applied only to diamonds 
of such a close approach to pure whiteness 



Naming of Precious Stones 153 

of body substance, as seen on edge in the paper 
that, when faced up and undimmed, they give 
such a strong play of prismatic blue that any 
slight trace of yellow in their substance is 
completely disguised, and the effect upon the 
eye is notably blue. This would be the case 
with ^stones of the grades from i through 4 
in the list above. Grades 5 and 6 might 
properly be called "fine white,' ^ and grades 7, 
8, and 9 simply "white.'' Grade 10 is fre- 
quently spoken of as "commercial white, ^' and 
grade 11 sometimes as "off color." Grade 12 
includes all degrees of brownness except the very 
light shades and the deep, pretty shades of 
the "fancy" browns. 

Rubies. Leaving the naming of the different 
colors of diamonds we come to the gems fur- 
nished us by the mineral known as corundum. 
As we have previously seen, this mineral occurs 
in many different colors and with wide differences 
of tint and shade in each of the principal colors. 
The best practice with regard to naming the 



154 Precious Stones 

corundum gems is to call the red material, 
when of a good, full red of pleasing shade, 
ruhy. The finest shades of blood red are 
usually called "Burmah rubies" because 
more rubies of this quality are found in Bur- 
mah than anywhere else. Any ruby of the 
required shade would, however, be called a 
Burmah ruby in the trade regardless of its 
geographical origin. The most desirable tint 
among Burmah rubies is that which is known as 
"pigeon blood" in color. This color is perhaps 
more accurately defined as like the color in the 
center of the red of the solar spectrum. Certain 
slightly deeper red rubies are said to be of 
"beef blood" color. The English are said to 
prefer these. Those of slightly lighter tint 
than pigeon blood are sometimes referred to 
as of "French color," from the fact that they 
are preferred by French connoisseurs. 

Rubies of dark, garnet-like shade are known 
as '*Siam rubies,'^ many such being found in 
that country. Light pinkish rubies are called 



Naming of Precious Stones 155 

''Ceylon rubies. ^^ It should be clearly kept 
in mind that all these "rubies" are of red 
corundum, and that in all their distinctive 
properties except color they are essentially 
similar. 

Sapphires. Corundum of fine blue color is 
known as ''sapphire/^ The "cornflower blue" 
seems to be most in favor at present. Such sap- 
phires are sometimes called ''Kashmir sap- 
phires^^ because many fine ones come from 
that State. "Ceylon sapphires^* are usually 
paler than the cornflower blue. "Montana 
sapphires ^^ are usually of greenish blue or 
pale electric blue. Such fine blue stones as 
are mined in Montana would be sold under 
another name according to the quality of 
their color, and not as "Montana sapphires." 
"Australian sapphires** are of a very deep, 
inky blue, and do not command a high price. 
Here again, as with rubies, the classification 
depends upon the color rather than upon the 
origin, although the geographical names that 



156 Precious Stones 

are used, correctly state the usual source of 
stones of the particular color. 

All corundums other than ruby and blue 
sapphire are usually called by the term "sap- 
phire, " with a qualifying adjective designating 
the color; thus we may have pink sapphire, 
golden sapphire, green sapphire, etc. When 
of very fine yellow color the yellow sapphire is 
sometimes called ^^ Oriental topaz' ^ by jewelers, 
the term "OrientaV' as thus used indicating that 
the material is corundum. We also have 
"Oriental amethyst" and "Oriental emerald' ' 
for the purple, and the fine green, and "Oriental 
aquamarine" for the light blue-green corundum. 
The yellow corundum is also sometimes called 
"King topaz," especially in Ceylon. Inferior 
sapphires of almost every conceivable color are 
frequently assorted in lots and sold as " fancy 
sapphires." Such lots, however, almost al- 
ways need reclassification as they often contain 
as many as a dozen mineral species besides 
corundum. 



Naming of Precious Stones 157 

Sapphires and rubies of minute tubular 
internal structure frequently display a beautiful 
six-pointed star when cut to a round-topped 
cabochon shape and exposed to direct sunlight 
or to light from any other single source. Such 
stones are named '^ star sapphire'" and "star 
rubyS 

The artificial rubies and sapphires should 
all be called scientific ruby or sapphire, and 
not "reconstructed'' or "synthetic'' as none 
are made to-day from small, real rubies, and 
as the process is in no sense a chemical syn- 
thesis. 

Chrysoberyl. Leaving the corundum gems 
we come next to chrysoberyl. When the gems 
furnished by this mineral are of a fine green 
by daylight, and of a raspberry red by artificial 
light, as is sometimes the case, they should 
be called " Alexandrites" (after the Csar Alex- 
ander II., in whose dominions, and on whose 
birthday, the first specimens are said to have 
been discovered) . When chrysoberyl is of fibrous 



158 Precious Stones 

or tubular internal structure it affords cat's-eyes 
(when cabochon cut), and these should be spe- 
cifically named as '' chrysoheryl cafs-eye'* to 
distinguish them from the less beautiful and 
less valuable quartz-cat' s-eyes. Other varieties 
of chrysoberyl (most of those marketed are of 
a greenish yellow color) are correctly named 
simply "chrysoberyls." Such stones are, how- 
ever, sometimes incorrectly called "chrysolite" 
by the trade, and this practice should be cor- 
rected, as the term chrysolite applies correctly 
only to the mineral olivine which gives us the 
peridot. 

Spinel. Next in the order that we have 
chosen comes "spinel.'" The more valuable 
spinels are of a red color that somewhat closely 
approaches the red of some rubies. Such 
red spinels should be called " RiLby spinel" 
(and not spinel ruby). The stones them- 
selves sometimes get mixed with corundum 
rubies (they are frequently found in the same 
gem gravels), and this makes it all the more 



Naming of Precious Stones 159 

necessary that both stones and names should be 
clearly distinguished. Some dealers call reddish 
spinels " Balas ruby^' (rose red), and orange red 
ones " ruhicelle.^^ Violet red spinel is sometimes 
called "almandine spinel/' It is very de- 
sirable that the name of the mineral species, 
spinel, should be used, together with a qualify- 
ing color adjective, in naming gems of this 
species, rather than such terms as "rubicelle, " 
" balas-ruby, " "spinel ruby," etc. 

Topaz. We come now to topaz. True, or 
precious topaz, as it is usually called, to dis- 
tinguish it from the softer and less valuable, 
yellow quartz, is seldom seen in the trade to-day. 
Jewelers almost always mean yellow quartz 
when they speak of "topaz." This is an 
unfortunate confusion of terms, and one which 
will be hard to eradicate. There is seldom 
any injustice done through this misnaming, as 
the price charged is usually a fair one for the 
material offered. Considerably higher prices 
would be necessary if true topaz was in question. 



i6o Precious Stones 

An instance from the writer's experience 
will serve to illustrate the confusion that 
exists in the trade as to what should be 
called topaz. A jeweler of more than ordinary- 
acquaintance with gems exhibited some fine 
brooch stones as specimens of topaz. On 
remarking that they were of course citrine 
quartz rather than true topaz, the author was met 
with the statement that the brooch stones 
were real topaz. In order to make clear 
to the dealer the difference between the two 
species, the author asked him if he hadn't some 
smaller topazes in stock that had cost him 
considerably more than the brooch stones. 
The dealer replied that he had some small 
wine yellow topazes for which he had paid 
more, and he produced them. The latter 
stones were true Brazilian topazes. Most 
of them had tiny, crackly flaws in them, as 
is frequently the case, and, as the writer pointed 
out to the dealer, they had been bought by the 
carat, whereas the large brooch stones had been 



Naming of Precious Stones i6i 

bought at a certain price per pennyweight. In 
fact the httle stones had cost more per carat 
than the larger ones had per pennyweight. 

The dealer was then asked if there must' 
not be some difference in the real nature of 
the two lots to justify paying more per carat 
for ^mall, imperfect stones than per penny- 
weight for large perfect ones. He of course 
acknowledged that it would appear reason- 
able that such was the case. He was next 
shown that his small true topazes scratched 
his large stones easily, but the large ones 
could get no hold upon the surfaces of the 
small ones. (It will be remem.bered that topaz 
has a hardness of 8, while quartz has a hard- 
ness of 7.) The explanation then followed 
that the two lots were from two entirely distinct 
minerals, topaz and quartz, and thatthe former 
was harder, took a somewhat better polish, and 
was more rare (in fine colors) than quartz. 
Of course the yellow quartz should be sold 
under the proper name, citrine quartz, (From 



i62 Precious Stones 

the same root that we have in ''citrus^* as 
applied to fruits. For example the "California 
Citrus Fruit Growers' Association," which sells 
oranges, lemons, grape fruit, etc. The color 
implication is obvious.) If the jeweler still 
wishes to use the term "topaz" because of the 
familiarity of the public with that name, then 
he should at least qualify it in some way. One 
name that is current for that purpose is "Span- 
ish topaz," another is "Quartz-topaz." Per- 
haps the latter is the least objectionable of the 
names that include the word topaz. 

Some of the wine yellow true topazes lose 
the yellow, but retain the pink component, 
on being gently heated. The resulting pink 
stone is rather pretty and usually commands 
a higher price than the yellow topazes. Such 
artificially altered topazes should be sold only 
for what they are, and probably the name 
"pinked topaz," implying, as it does, that 
something has been done to the stone, is as 
good a name as any. There is, however, little 



Naming of Precious Stones 163 

chance of fraud in this connection, as natural 
pink topazes are not seen in the trade, being very 
rare. 

Some bluish green topaz is said to be sold as 
aquamarine, and this confusion of species 
and of names should, of course, be stopped by 
an actual determination of the material as to its 
properties. Lacking a refractometer, the widely 
differing specific gravities of the two minerals 
would easily serve to distinguish them. 



LESSON XX 
THE NAMING OF PRECIOUS STONES {Concluded) 

Beryl, Emerald, Aquamarine. Coming now 
to heryl we have first emerald, then aquamarine, 
then beryls of other colors to consider. There 
is too often a tendency among dealers to confuse 
various green stones, and even doublets, under 
the name emerald. While the price charged 
usually bears a fair relation to the value of the 
material furnished, it would be better to offer 
tourmaline, or peridot (the mineral name of 
which is olivine), or demantoid garnet (some- 
times wrongly called "Olivine"), or "emerald 
doublets," or emerald or "imitation emerald," 
as the case might be, under their own names. 

There are no true "synthetic" or "scien- 
tific" or "reconstructed" emeralds, and none 

of these terms should be used by the trade. 
164 



Naming of Precious Stones 165 

There has been an effort made in some cases to 
do business upon the good reputation of the 
scientific rubies and sapphires, but the products 
offered, when not out and out glass imitations, 
have usually been doublets or triplets, consisting 
partly of some pale, inexpensive, natural min- 
eralf such as quartz or beryl, and a layer of deep 
green glass to give the whole a proper color. 
All attempts to melt real emerald or beryl have 
yielded only a heryl glass, softer and lighter 
than true emerald, and not crystalline, but 
rather glassy in structure. Hence the names 
"reconstructed," "synthetic" and "scientific" 
should never be applied to emerald. 

The light green and blue green beryls are 
correctly called aquamarines, the pale sky- 
blue beryls should be named simply blue beryl. 
Yellow beryl may be called golden beryl, or 
it may be called '^heliodor,^' a name that was 
devised for the fine yellow beryl of Madagascar. 
Beautiful pink beryl from Madagascar has 
been called "morganite," a name that deserves 



i66 Precious Stones 

to live in order to commemorate the great 
interest taken by J. Pierpont Morgan in collect- 
ing and conserving for future generations 
many of the gems in the American Museum of 
Natural History in New York. 

Zircon. We now come to a number of min- 
erals slightly less hard than beryl, but harder 
than quartz, and zircon is perhaps as hard 
as any of these, so it will be considered next. 
Red zircon, which is rare, is properly called 
"hyacinth.'^ Many Hessonite garnets (cinna- 
mon stones) are incorrectly called hyacinths, 
however. The true hyacinth has more snap 
and fire owing to its adamantine surface luster 
and high dispersive power, as well as to its high 
refractive index. A true hyacinth is a beauti- 
ful stone. Golden yellow zircons are correctly 
called "jacinths. " Artificially whitened zircons 
(the color of which has been removed by heat- 
ing) are known as "jargoons" or sometimes 
as "Matura diamonds." All other colors in 
zircon should be named simply zircon, with 



Naming of Precious Stones 167 

a color adjective to indicate the particular 
color as, "brown zircon," etc. 

Tourmaline. Tourmaline furnishes gems of 
many different colors. These are all usually 
called simply tourmaline, with a color adjective 
to specify the particular color, as, for ex- 
ample, the "pink tourmaline" of California. 
Red tourmaline is, however, sometimes called 
"rubelite/^ and white tourmaline has been 
called "achroite/* The latter material is sel- 
dom cut, and hence the name is seldom seen or 
used. 

Garnet. We may next consider the garnets, 
as most of them are somewhat harder than 
quartz. As was said in Lesson XVIII. in 
our study of mineral species, there are sev- 
eral types of garnets, characterized by sim- 
ilarity of chemical composition, or at least 
by analogy of composition, but, having specific 
differences of property. The names used by 
jewelers for the several types of garnets ought 
to be a fairly true indication as to the type in 



i68 Precious Stones 

hand in a particular case. At present there is 
considerable confusion in the naming of garnets. 
The most common practice is to call all garnets 
of a purplish red color ' ' almandines. ' ' As many 
such garnets belong to the mineral species 
almandite garnet, there is little objection to 
the continuance of this practice. The some- 
what less dense, and less hard blood red garnets 
are properly called "pyrope garnets" (literally 
"fire" garnets). Many of the Arizona garnets 
belong in this division. The term "Arizona 
rubies'' should not be used. As was said under 
ruby, nothing but red corundum should receive 
that title. Similarly the pyrope garnet of the 
diamond mines of South Africa is incorrectly 
called "Cape ruby." Pyrope and almandite 
garnet tend to merge in composition and in 
properties, and the beautiful "Rhodolite'' gar- 
nets of Macon County, North Carolina, are be- 
tween the two varieties in composition, in 
color, and in other properties. 

Hessonite garnet furnishes yellowish red and 



Naming of Precious Stones 169 

brownish red stones, which are sometimes also 
called "cinnamon stones." They are also 
frequently and incorrectly called jacinth or 
hyacinth, terms which, as we have seen, should 
be reserved for yellow and red zircon, respec- 
tively. 

Andradite garnet furnishes brilliant green 
stones, which have been incorrectly named 
"Olivines" by the trade. The name is un- 
fortunate as it is identical with the true name 
of the mineral which gives us peridot. The 
name does not even suggest the color of these 
garnets correctly, as they are seldom olive 
green in shade. As the scarcity of fine speci- 
mens and their great beauty make a fairly high 
price necessary, the public would hardly pay it 
for anything that was called "garnet," as gar- 
nets are regarded as common and cheap. Per- 
haps the adoption of the name " Demantoid'* 
might relieve the situation. The stones are fre- 
quently referred to as "demantoid garnets" 
on account of their diamond-like luster and 



170 Precious Stones 

dispersion. The use of "demantoid" alone, 
if a noun may be made from the adjective, would 
avoid both the confusion with the mineral 
olivine, and the cheapening effect of the word 
garnet, and would at the same time suggest 
some of the most striking properties of the 
material. 

"Spodumene" furnishes pink to lilac "Kun- 
zite," named after Dr. George F. Kunz, the gem 
expert, and for a time an emerald green variety- 
was had from North Carolina which became 
known as "Hiddenite," after its discoverer, 
W. E. Hidden. No confusion of naming seems 
to have arisen m regard to this mineral. 

The next mineral in the scale of hardness 
is quartz. (Hardness 7.) When pure and 
colorless it should be called "rock crystal." 
Purple quartz is of course amethyst. Some 
dealers have adopted a bad practice of calling 
the fine deep purple amethyst "Oriental" 
amethyst, which should not be done, as the term 
"Oriental" has for a long time signified a corun- 



Naming of Precious Stones 171 

dum gem. As Siberia has produced some very 
fine amethysts, the term "Siberian amethyst'* 
would be a good one to designate any especially 
fine gem. 

Quartz Gems. We have already considered 
the naming of yellow quartz in connection with 
topaa. ''Citrine quartz'' is probably the best 
name for this material. If it is felt that the 
name "topaz " must be used, the prefix "quartz'* 
should be used, or perhaps "Spanish topaz" 
will do, but some effort should be made to 
distinguish it from the true precious topaz. In 
addition to amethyst and citrine quartz we 
have the pinkish, milky quartz known as "rose 
quartz.'' This is usually correctly named. 

" Cat's-eye" is a term that should be reserved 
for the Chrysoberyl variety, and the quartz 
variety shoiild always be called "quartz- 
cat's-eye." "Tiger's-eye" is a mineral in which 
a soft fibrous material has been dissolved away, 
and quartz has been deposited in its place. 
"Aventurine quartz'' is the correct name for 



172 Precious Stones 

quartz containing spangles of mica. Clear, 
colorless pebbles of quartz are sometimes cut for 
tourists. Such pebbles are frequently misnamed 
"diamonds" with some prefix, as for example 
"Lake George diamonds, " etc. Among the 
minutely crystalline varieties of quartz we 
have the clear red, which should be called 
"carnelian,'' the brownish red ''sard," the green 
"chrysoprase," the leek green "prase," and the 
brighter green "plasma." The last three are 
not so commonly seen as the first two, and 
frequently the best-colored specimens are ar- 
tificially dyed. 

"Jasper," a material more highly regarded 
by the ancients than at present, is mainly 
quartz, but contains enough earthy mate- 
rial to make it opaque. "Bloodstone" is a 
greenish chalcedony with spots of red jasper. 

"Agates" are banded chalcedonies, the va- 
riety called "onyx" having very regular bands, 
and the "sardonyx" being an onyx agate 
in which some of the bands are of reddish sard. 



Naming of Precious Stones 173 

Just as we considered opal with quartz 
(because of its chemical similarity) when 
discussing mineral species, so we may now 
consider the proper naming of opals here. 
''Precious opal'' is distinguished from "com- 
mon opaV by the beauty of its display rather 
than^by any difference in composition. The 
effect is of course due to the existence of thin 
films (probably of material of slightly different 
density), filling what once were cracks in the 
mass. The rainbow colors are the result of 
interference of light (see a college text on phy- 
sics for an explanation of interference). The 
varying thickness of these films gives varying 
colors, so different specimens of opal show very 
different effects. The differences of distribu- 
tion of the films within the material also cause 
variations in the effects. Hence we have hardly 
any two specimens of opal that are alike. 

There are, however, certain fairly definite 
types of opal and jewelers should learn to apply 
correct names to these types. Most prominent 



174 Precious Stones 

among the opals of to-day are the so-called 
''Black opals'' from New South Wales. These 
give vivid flashes of color out of seeming dark- 
ness. In some positions the stones, as the name 
implies, appear blue-black or blackish-gray. 
By transmitted light, however, the bluish stones 
appear yellow. Owing to the sharp contrast 
between the >dark background and the flash- 
ing spectrum colors, black opals are most at- 
tractive stones and fine specimens command 
high prices. One fine piece, which was on ex- 
hibition at the Panama-Pacific Exposition was 
in the shape of an elongated shield, about i^ 
inches by 1 3^ inches in size and rather flat and 
thin for its spread. It gave in one position a 
solid surface of almost pure ruby red which 
changed to green on tipping the stone to the 
opposite direction; $2,000 was asked for the 
piece. 

''White opaV* is the name applied to the 
lighter shades of opal which do not show the 
bluish-black effect in ^ny position, "Harlequin 



Naming of Precious Stones 175 

opaV has rather large areas of definite colors 
giving somewhat the effect of a map of the 
United States in which the different States are 
in different colors. 

''Fire opal" is an orange-red variety. It 
has some "play" of colors in addition to its 
orange-red body color. 

"Opal Matrix" has tiny specks and films 
of precious opal distributed through a dark 
volcanic rock and the mass is shaped and 
polished as a whole. 

Jade. ' ' Jade ' ' should next receive attention. 
It is a much abused term. Under it one may 
purchase jadeite, nephrite, bowenite, amazonite, 
or frequently simply green glass. The use of the 
word ought to be confined to the first two min- 
erals mentioned, namely, jadeite and nephrite, 
for they only possess the extreme toughness to- 
gether with considerable hardness that we expect 
of jade. Bowenite, while tough, is relatively 
soft and amazonite is brittle and also easily 
cleavable, while glass is both soft and brittle. 



176 Precious Stones 

Peridot and Olivine. The mineral ''olivine'' 
gives us the "peridot" (this name should be kept 
for the deeper bottle green stones), and the olive 
green gems of this same mineral may cor- 
rectly be called "olivine" or "chrysolite." 
As was explained under garnet, jewelers fre- 
quently use the term "olivine" to designate 
demantoid garnet. The term chrysolite is also 
sometimes incorrectly used for the greenish- 
yellow chrysoberyl. 

Feldspar Gems. Among the minerals softer 
than quartz, which are used as gems, we have 
also "feldspar," which gives us "moonstone," 
" Labradorite," and "Amazonite." 

An opalescent form of chalcedony is fre- 
quently gathered on California beaches and 
polished for tourists under the name of "Cali- 
fornia Moonstone." This name is imfortu- 
nately chosen as the material is not the same as 
that of true moonstone and the effect is not so 
pronounced or so beautiful. The polished 
stones show merely a milky cloudiness without 



Naming of Precious Stones 177 

any of that beautiful sheen of the true moon- 
stone. "Labradorite" is usually correctly 
named. "Amazonite" was originally mis- 
named, as none is found along the river of that 
name. The term has come into such general 
use, however, that we shall probably have to 
continue to use it, especially as no other name 
has come into use for this bluish-green feldspar. 
As has already been said, amazonite is sometimes 
sold as "jade, " which is incorrect. 

Malachite, Azurite, and Lapis Lazuli. Mal- 
achite and azurite are usually correctly 
named, but " lapis lazuli" is a name that is 
frequently misused, being applied to crackled 
quartz that has been stained with Prussian 
blue, or some other dye, to an unconvincing 
resemblance to true lapis. Such artificially 
produced stones are sometimes sold as *' Swiss 
lapis." They are harder than true lapis 
and probably wear much better in exposed 
ornaments, but they are not lapis and are never 
of equal color, and names should not be misused, 



1/8 Precious Stones 

and especially is this true in a trade where the 
public has had to rely so completely upon the 
knowledge and the integrity of the dealer. 

With the increase of knowledge about pre- 
cious stones that is slowly but steadily growing 
among the public, it becomes more than ever 
necessary for the jeweler and gem dealer to 
know and to use the correct names for all pre- 
cious stones. The student who wishes to learn 
more about the matter will have to cull his 
information from many different works on gems. 
G. F. Herbert-Smith, in his Gem Stones, gives a 
three and one half page chapter on "No- 
menclature of Precious Stones" (Chap. XIII, 
pp. 109-112). The present lesson has attempt- 
ed to bring together in one place material from 
many sources, together with some suggestions 
from the author. 



LESSON XXI 

WHERE PRECIOUS STONES ARE FOUND 

Occurrence of Diamond. Every dealer in 
precious stones should know something of the 
sources of the gems that he sells. The manner 
of the occurrence of the rough material is also a 
matter of interest. It will therefore be the 
purpose of this lesson to give a brief account of 
the geographical sources of the principal gems 
and of their mode of occurrence in the earth. 

For the sake of uniformity of treatment 

we will once more follow the descending order 

of hardness among the gems and we thus 

begin by describing the occurrence of diamond. 

It will be of interest to note first that the earliest 

source of the diamond was India, and that for 

many years India was almost the sole source. 

Tavernier tells us that the diamond mining 
179 



i8o Precious Stones 

industry was in a thriving state during the 
years from 1640 to 1680, during which time he 
made six journeys to India to purchase gems. 
He speaks of Borneo as another source of 
diamonds, but most of the diamonds of that 
time were furnished by India. 

" Golcondas." Indian diamonds were note- 
worthy for their magnificent steely blue- white 
quality and their great hardness, and occasion- 
ally one comes on the market to-day with an 
authentic pedigree, tracing its origin back 
to the old Indian mines, and such stones 
usually command very high prices. One of 
a little over seven and one half carats in weight, 
in the form of a perfect drop brilliant, has 
lately been offered for sale at a price not far 
from $1,000 per carat. Such diamonds are 
sometimes called "Golcondas" because one of 
the mining districts from which the fine large 
Indian stones came was near the place of that 
name. vSome of the stones from the Jagersfon- 
tein mine in South Africa resemble the Golcon- 



Where Precious Stones are Found i8i 

das in quality. Many of the large historical crown 
diamonds of Europe came from the Indian mines. 

The stones were found in a sedimentary 
material, a sort of conglomerate, in which 
they, together with many other crystalline 
materials, had become imprisoned. Their origi- 
nal source has never been determined. They 
are therefore of the so-called "River" type 
of stone, having probably been transported 
from their original matrix, after the disinteg- 
ration of the latter, to new places of deposit, by 
the carrying power of river waters. 

The Indian mines now yield very few stones. 
The United States Consular reports occasionally 
mention the finding of a few scattered crystals 
but the rich deposits were apparently worked 
out during the seventeenth century and the 
early part of the eighteenth century. 

In 1725 and in the few following years the 
Brazilian diamond fields began to supersede 
those of India. Like the latter, the Brazilian 
fields were alluvial, that is, the materials 



1 82 Precious Stones 

were deposited by river action after having 
been carried to some distance from their original 
sources. 

Brazilian Diamonds. The diamonds of Brazil 
also resembled those of India in quality, being 
on the average better than those of the present 
South African mines. It may be added that 
even the African diamonds that are found in 
"river diggings" average better in quality than 
those of the volcanic pipes which form the 
principal source of the world's supply to-day, 
There seems to be a superabundance of iron 
oxide in the rocks of the African mines and in 
the diamonds themselves, imparting yellow or 
brownish tints to the material. The "River" 
stones seem to have lost this color to a consider- 
able extent, if they ever had it. Possibly 
long extraction with water has removed the very 
slightly soluble coloring material. Whatever 
the cause of their superiority "River" stones 
have always been more highly regarded than 
stones from the volcanic pipes. 



Where Precious Stones are Found 183 

Brazil furnished the world's principal supply 
of diamonds until the discovery of the African 
stones in 1867. At present relatively small 
numbers of Brazilian stones reach the world's 
markets. Most of these come from the great 
Bahia district (discovered in 1844) rather than 
from the older mines of Brazil. The present 
Brazilian stones average of small size. They are, 
however, of very good quality as a rule. A few 
green stones are found in Brazil and these may be 
of an absinthe-green or of a pistachio-green tint. 

Australian and American Sources. While a 
few diamonds now come on the market from 
New South Wales, and while an occasional stone 
is found in the United States (usually in glacial 
drift in the north central States, or in volcanic 
material somewhat resembling that of South 
Africa in Arkansas) yet the world's output now 
comes almost entirely from South Africa and 
mainly from the enormous volcanic pipes of 
the Kimberly district and those of the Premier 
Co. in the Transvaal. 



184 Precious Stones 

South African Diamonds. The nature of the 
occurrence of diamond in the "pipes" of South 
Africa is so well known to all who deal in dia- 
monds to-day that but little space need be de- 
voted to it. The "blue ground, " as the rock in 
which the diamonds are found is called, seems 
to have been forced up from below, perhaps 
as the material of a mud volcano, bringing 
with it the diamonds, garnets, zircons, and 
the fifty or more other minerals that have 
been found in the blue ground. • The frag- 
mentary character of some of these minerals 
would indicate that the blue ground was not 
their original matrix. How the diamonds 
originally crystallized and where, is still prob- 
ably a matter for further speculation. 

While at first the mines were worked, like 
quarries, from the surface, and while the great 
Premier mine is still so worked, most of the 
present mines are worked by sinking shafts 
in the native rock outside of the blue ground 
and then tunneling into the diamond-bearing 



Where Precious Stones are Found 185 

rock laterally, removing it to the surface, allow- 
ing it to weather on the "floors" until it 
crumbles, then crushing and washing it and 
concentrating the heavy minerals by gravity 
methods. Large diamonds are then picked out 
of the concentrates by hand and small ones 
ar^ fragments are removed by the "greas- 
ers, " which are shaking tables heavily smeared 
with grease over which the concentrates are 
washed and to which diamond alone, of all the 
minerals in the concentrate, sticks. The grease 
is periodically removed and melted, and the 
diamonds secured. The grease can then be 
used again. 

German South West Africa furnishes a 
considerable output of very small diamonds, 
which are found in dry sand far from any 
present rivers. These diamonds cut to splendid 
white melee and the output is large enough to 
make some difference in the relative price of 
small stones as compared to large ones. The 
South West African field seldom yields a stone 



i86 Precious Stones 

that will afford a finished quarter-carat dia- 
mond. 

Rubies. Passing on to the occurrence of the 
corundum gems we will consider first the ruhy. 
Most fine rubies come from Burmah. The 
district in which they are found is near Mogok. 
Practically all the fine pigeon-blood rubies come 
from this district. The fashion for red stones 
being for the time little in evidence rubies are not 
now in great demand. This cessation of demand 
can hardly be laid to the competition of the 
scientific ruby, for the sapphire is now very 
much in vogue, yet scientific sapphires re- 
semble the natural ones even more closely 
than do the rubies. 

Siam furnishes a considerable number of 
dark garnet-like rubies. These do not com- 
mand high prices. They are, however, some- 
times very beautiful, especially when well cut 
for brilliancy, and when in a strong light. 

Ceylon furnishes a few rubies and a few red 
corundums have been found in North Carolina. 



Where Precious Stones are Found 187 

The Burmese rubies appear to have been 
formed in a limestone matrix, but most of 
those obtained are gotten from the stream 
beds, where they have been carried by water 
after weathering out from the mother rock. 

The rubies of Ceylon, too, probably origin- 
ated in a limestone matrix, but are sought in 
stream gravels. 

Sapphires. Fine blue sapphires originate in 
Siam in larger numbers than in any other local- 
ity. Kashmir, in India, also supplies splen- 
did specimens of large size. Ceylon, too, 
furnishes a good deal of sapphire, but mostly 
of a lighter color than the Kashmir sapphire. 
The Ceylon sapphires are found in the streams, 
but originate in rock of igneous origin. 

Montana furnishes considerable quantities 
of sapphire, some of which is of very good color. 
It is, of course, as good as the Oriental if of equal 
color, being of the same material. The better 
colored sapphire from Montana is mined from 
the rock. Most of the sapphires found in the 



1 88 Precious Stones 

river gravels near Helena, Mont., are greenish- 
blue or of other colors, and not of fine blue. 

Queensland and Victoria in Australia supply 
considerable quantities of sapphire. When 
blue the Australian sapphire is usually too dark 
to be very valuable. The golden and other 
"fancy" sapphires of the trade come largely 
from the Ceylon gravels. Siam yields silky- 
brown stones and some fine green ones. Some 
of the Australian sapphires when cut in certain 
directions yield green stones. 

Chrysober}^. Chrysoberyl of the variety 
Alexandrite now comes mainly from Ceylon, 
although formerly from the Ural Mountains. 

The cat's-eyes also come chiefly from Ceylon. 

The yellowish-green chrysoberyls (which 
jewelers sometimes call chrysolite) come both 
from Ceylon and from Brazil. They are fre- 
quently found in papers of "fancy sapphires" 
or "fancy color stones," so called. 

Spinel. Spinels are found along with ruby in 
Burmah and in Siam and they also occur 



Where Precious Stones are Found 189 

in the gem gravels of Ceylon. Limestone is 
the usual matrix of spinel, although it is more 
often mined in gravels resulting from the 
weathering of the matrix. 

Topaz. True topaz, of wine-yellow color, 
comes mostly from Brazil. Ceylon also fur- 
ni^es yellow topaz. Asiatic Russia furnishes 
fine large blue or blue-green crystals resembling 
aquamarine in appearance. Most of the topaz 
found in other localities is pale or colorless. 
Several of our western States, notably Utah, 
Colorado, and California, furnish colorless topaz. 
Mexico and Japan also produce it. It is seldom 
cut, for, while producing a rather brilliant stone, 
it has little "fire" and is therefore not very 
attractive. 

Emerald and Aquamarine. Beryl of the 
emerald variety is exceedingly scarce in the 
earth. Most of the best emerald comes from 
Colombia, South America. Large crystals of 
paler color come from the Urals. 

Like ruby and spinel, emerald usually origin- 



190 Precious Stones 

ates in limestone. One is tempted to suspect 
that these stones are of aqueous origin and that 
sapphires, and beryl, other than emerald, are 
more likely of igneous origin. 

Beryls of the aquamarine type occur in 
many places, but usually of too pale a tint, 
or too imperfect, to be worthy of cutting. 
Fine gem beryl of blue and blue-green tints 
comes from Siberia and from several places in 
the Ural Mountains on their Asiatic slopes. 

The Minas Garaes district of Brazil, famous 
for all kinds of gem stones, furnishes most of 
the aquamarine of commerce. The pegmatite 
dikes of Haddam Neck, Conn., of Stoneham, 
Me., and of San Diego County, CaL, have fur- 
nished splendid aquamarine and other beryl. 
These dikes, according to the geological evi- 
dence, are the result of the combined action of 
heat and water. Thus both melting and dissolv- 
ing went on together and as a result many fine 
gem minerals of magnificent crystallization were 
formed during the subsequent cooling. The 



Where Precious Stones are Found 191 

longer the cooling lasted and the more free 
space for growth the crystals had, the larger 
and more perfect they got. The author has 
himself obtained finely crystallized aquamarine 
and tourmaline from the Haddam, Conn., 
locality and the best specimens there occur 
in ^'pockets" or cavities in the coarse granite. 
Within, these pockets are lined with crystals 
of smoky quartz, tourmaline, beryl, and other 
minerals. Sometimes crystals occur in mud or 
clay masses inside the cavities and such crys- 
tals, having been free to grow uninterruptedly 
in every direction, were perfect in form, being 
doubly terminated, and not attached any- 
where to the rock. 

Madagascar has in recent years furnished 
the finest pink beryl, which has been named 
Morganite. Yellow beryl (Heliodor) and aqua- 
marine also occur in Madagascar. 

Zircon. Zircon comes on the market mainly 
from Ceylon. It deserves to be as much 
esteemed in this country as it is in Ceylon, for 



192 Precious Stones 

its optical properties are such that it is a very 
snappy stone. Some of the colors in which 
it occurs, such as the golden browns, lend 
themselves nicely to the matching of gems 
and garments, and, with the growth of edu- 
cation in such matters, jewelers would do well 
to get better acquainted with the possibilities 
of zircon and to introduce it to their customers. 
The supply from Ceylon is sufficient to justify 
popularizing the stone. Small zircons are found 
in almost every heavy concentrate, as, for exam- 
ple, in the concentrates of the diamond mines 
of South Africa, and in those of gold placers 
in many places. The rough stones resemble 
rough diamonds in luster and are sometimes 
mistaken for diamonds. 

Garnets. Garnets of various types are found 
widely distributed in nature. Perhaps the Bo- 
hemian supply is best known, having furnished a 
host of small stones which have usually been 
rose cut for cluster work or made into beads. 
The Bohemian garnets are of the pyrope or 



Where Precious Stones are Found 193 

fire-red type. Relatively few large stones of 
sufficient transparency for cutting are produced 
in the Bohemian mines. The so-called "Cape 
rubies" of the diamond mines of South Africa 
are pyrope garnets and some large and fine 
ones are found. The "Arizona rubies" are 
pyCDpe garnets, and while seldom of notable 
size, some are of very fine color, approaching 
deep rubies, and the color remains attractive 
by artificial light. 

Almandite garnet, the "almandine" of the 
jeweler is less abundant than pyrope, when 
of gem quality. Ceylon furnishes some and 
India furnishes perhaps more. Brazil, from 
its prolific gem gravels at Minas Novas, supplies 
good almandite, and smaller quantities are 
found in many different localities. 

Hessonite garnet, the cinnamon stone or 
"hyacinth" (incorrect) of the trade, comes 
mainly from Ceylon. 

Andradite garnet, of the variety known as 

demantoid, from its diamond-like properties, 
13 



194 Precious Stones 

and which is usually sold under the mis- 
leading name "olivine "in the trade, comes from 
the western slopes of the Ural Mountains. 

Tourmaline. Gem tourmaline comes from 
Ceylon, from Madagascar, from the Ural 
Mountains, from Brazil, from Maine, from 
Connecticut, and from California. 

The Ceylon tourmalines are mostly yel- 
low or yellowish-green, sometimes fine olive- 
green. Those from the Urals may be 
pink, blue or green. Brazilian tourmalines 
are usually green, but sometimes red. In 
fact in many localities several colors of tour- 
maline are usually found together and it may 
be that a single crystal will be green in most of 
its length but red or pink tipped. Some 
crystals have a pink core and a green exterior. 
The author has found both of the two latter 
types in the Haddam, Conn., tourmalines, and 
on one occasion was surprised to get back a 
wine-colored tourmaline from a cutter to whom 
he had sent a green crystal. There was but 



Where Precious Stones are Found 195 

a thin shell of the green material on the outside 
of the crystal. 

Some of the Madagascar tourmaline is of 
a fine brownish-red, almost ' as deep as a 
light garnet, and much clearer than most 
garnet. 

Would it not be fitting on account of its 
occurrence in several localities in the United 
States, for Americans to use more tourmaline 
in their jewels? The quality of some of the 
tourmalines of Maine, and of California especi- 
ally, is not excelled by tourmaline from any 
other locality. Some of the Maine tourmaline 
is of a delightful, slightly bluish-green tint that 
almost approaches emerald. 

Kunzite. Spodumene, of the variety kun- 
zite, comes from San Diego County, California. 

Quartz Gems. Coming now to the quartz 
gems we find amethyst and citrine, or golden 
quartz widely distributed so that only the local- 
ities that furnish the better grades of these 
stones need be mentioned. Siberia and Uruguay 



'196 Precious Stones 

furnish fine amethyst. Brazil also furnishes 
large quantities of very good quality. 

Amethyst. The chief charm of the Siberian 
amethyst lies in its large red component, 
which enables it to change from a deep grape- 
purple by daylight to a fine red by artificial 
light that is rich in red rays, and poor in blue 
ones. The paler types of amethysts that were 
once esteemed, probably for lack of the rich deep 
variety, become gray in appearance and much 
less lovely under artificial light. India furnishes 
some amethysts, and papers of "fancy color 
stones " containing native cut gems from Ceylon, 
frequently contain amethysts, but Brazil, Uru- 
guay, and Siberia furnish the great bulk of the 
stones that are regarded as choice to-day. 

Yellow Quartz. Citrine or golden quartz 
comes mainly from Brazil. The "Spanish 
topaz" is sometimes the result of heating 
smoky quartz from Cordova province in Spain. 
Our own western mountains furnish consider- 
able yellow and smoky quarts fit fpr cutting. 



Where Precious Stones are Found 197 

Rose Quartz. Rose quartz of the finest 
quality comes from South Dakota. Bavaria, 
the Ural Mountains, and Paris, Maine, have also 
furnished it. 

Agate. Agates of the finest types, such as 
camelian and sard, come principally from 
Bsazil and from India. 

Opal. Opals now come most largely from 
Australia, the Hungarian mines yielding but 
few stones at present. The fine black opals 
of New South Wales are unsurpassed by 
any that have ever been found elsewhere, 
Mexico furnishes considerable opal, and is 
notable for its fine "fire opal " or "cherry opal. " 

Jade. Most of the jade of the variety ne- 
phrite that is obtained to-day comes from 
several of the provinces of China or from Siberia 
or from Turkestan. A dark-green nephrite 
comes from New Zealand. 

Jade of the jadeite variety, which is hard- 
er than nephrite and more highly valued, is 
rare. The best specimens come from Upper 



198 Precious Stones 

Burmah. It is also found in China and in 
Tibet. 

Peridot. Peridot, and the brighter olivine or 
chrysolite, while of the same mineral species, 
do not seem to occur together. The darker 
bottle-green specimens come from the Island of 
St. John in the Red Sea. It is said that many 
of the finer peridots now available have been 
recut from old stones mined many years ago. 
_ Queensland supplies light-green chrysolite, 
and Arizona a yellowish-green variety. Light- 
green stones have been found near the ruby 
mines of Upper Burmah. 

Moonstone. Moonstone comes mainly from 
Ceylon. The native cut specimens are sent 
here and recut, as, when native cut, the direc- 
tion of the grain is seldom correct to produce 
the moonlight effect in symmetrical fashion. 
The native cutters apparently try to retain 
all the size and weight that is possible, regard- 
less of the effect. 

Turquoise. Turquoise of the finest blue and 



Where Precious Stones are Found 199 

most compact texture (and hence least subject 
to color change) comes from the province 
of Khorassan in Persia. Several of our western 
states supply turquoise of fair quality, notably 
New Mexico, Arizona, Nevada, and California. 

Lapis Lazuli. Lapis Lazuli comes from Af- 
gli^nistan, from Siberia, and from South 
America. 

Malachite. Malachite is found in many 
copper mines, but principally in those of the 
Ural Mountains. 

Azurite. Azurite is found in the Arizona 
mines and in Chessy, in France (hence the name 
chessylite, sometimes used instead of azurite). 

References. Students who wish to get a 
fuller account of the occurrence of precious 
stones should run through G. F. Herbert- 
Smith's Gem-Stones under the different varieties. 
This work is the most recent authentic work of 
a strictly scientific character. Dr. George F. 
Kunz's Gems and. Precious Stones of North 



200 Precious Stones 

America gives a detailed account of all the finds 
in North America up to the time of publication. 
Many of these are of course of little commercial 
importance. The Mineral Resources of the 
United States contains annually a long accoimt 
of the occurrences of gem materials in this 
country. A separate pamphlet containing only 
the gem portion can be had gratis from the office 
of the United States Geological Survey, Wash- 
ington, D. C. 



LESSON XXII 

HOW ROUGH PRECIOUS STONES ARE CUT 

i^ough Precious Stones. John Ruskin, who 
had the means to acquire some very fine natural 
specimens of gem material was of the opinion 
that man ought not to tamper with the wonder- 
ful crystals of nature, but that rather they 
should be admired in the rough. While one 
can understand Ruskin's viewpoint, neverthe- 
less the art of man can make use of the optical 
properties of transparent minerals, properties 
no less wonderful than those exhibited in crys- 
tallization, and indeed intimately associated 
with the latter, and, by shaping the rough ma- 
terial in accordance with these optical proper- 
ties, greatly enhance the beauty of the gem. 

No material illustrates the wonderful improve- 
ment that may be brought about by cutting 

201 



202 Precious Stones 

and polishing better than diamond. In the 
rough the diamond is less attractive in appear- 
ance than rock crystal. G. F. Herbert-Smith 
likens its appearance to that of soda crystals. 
Another author likens it to gum arable. The 
surface of the rough diamond is usually ridged by 
the overlapping of minute layers or strata of the 
material so that one cannot look into the clear 
interior any more than one can look into a bank, 
through the prism-glass windows that are so 
much used to diffuse the light that enters by 
means of them. Being thus of a rough exterior 
the uncut diamond shows none of the snap and 
j&re which are developed by proper cutting. 

As the diamond perhaps shows more improve- 
ment on being cut than any other stone, and as 
the art of cutting the diamond is distinct from 
that of cutting other precious stones, both in the 
method of cutting and in the fact that the 
workers who cut diamonds cut no other precious 
stones, it will be well to consider diamond 
cutting separately. 



How Rough Stones are Cut 203 

Before discussing the methods by which 
the shaping and polishing are accomplished 
let us consider briefly the object that is in 
view in thus altering the shape and smoothing 
the surface of the rough material. 

How Cutting Increases Brilliancy. Prima- 
rily ihe object of cutting a diamond is to make 
it more brilliant. So true is this that the 
usual form to which diamonds are cut has come 
to be called the brilliant. The adjective has 
become a noun. The increased brilliancy is due 
mainly to two effects: First, greatly increased 
reflection of light, and second, dispersion of 
light. The reflection is partly external but 
principally internal. 

Taking up first the internal reflection which is 
responsible for most of the white brilliancy of the 
cut stone we must note that it is a fact that light 
that is passing through any transparent material 
will, upon arriving at any polished surface, 
either penetrate and emerge or else it will be 
reflected within the material, depending upon 



204 



Precious Stones 



the angle at which the light strikes the surface. 
For each material there is a definite angle out- 
side of which light that is passing as above 



A 




B 



Fig. 9 

A B represents the back surface of a piece of 
diamond. 

C £) is a line perpendicular to A B. 

Angle C D E IS about 24 degrees. 

Dotted line, F D H represents the course taken 
by a ray of light which is totally reflected at £) 
in such fashion that angle FDA equals angle 
H D B. 

Any light proceeding towards A B but between 
E and C, would fail to be totally reflected. Most 
of it would penetrate A B. 



described, is totally reflected within the material. 
Total Reflection. For diamond this critical 
angle, as it is called, is very nearly 24° from a 
perpendicular to the surface. If now, we shape 
a diamond so that most of the light that enters 
it from the front falls upon the first back siu*- 
face that it meets, at an angle greater than 24° 



How Rough Stones are Cut 205 

to a perpendicular to that surface, the light will 
be totally reflected within the stone. The angle 
at which it is reflected will be the same as that 
at which it meets the surface. In other 
words the angles of incidence and of reflection 
are equal. See Fig. 9 for an illustration of this 
point. 

Theory of the "Brilliant." In the usual 
"brilliant" much of the light that enters 
through the front surface is thus totally reflected 
from the first rear facet that it meets and 
then proceeds across the stone to be again 
totally reflected from the opposite side of 
the brilliant. This time the light proceeds 
toward the top of the stone. See Fig. 10 — 
(From G. F. Herbert-Smith's Gem Stones). 

The angles of the top of a brilliant are 
purposely made so flat that the up coming 
light fails to be totally reflected again and 
is allowed to emerge to dazzle the beholder. 
In the better made brilliants the angle that the 
back slope makes with the plane of the girdle is 



2o6 



Precious Stones 



very nearly 41'' and the top angle, or angle of 
the front slope to the plane of the girdle is about 
35°. Such well made brilliants when held up to 
a bright light appear almost black — that is, 




Fig. 10. — Course of the ITays of Light] 
Passing Through a Brilliant. 



they fail to pass any of the light through them 
(except through the tiny culet, which, being 
parallel to the table above, passes light that 
comes straight down to it). 

In other words, instead of allowing the 
light to penetrate them, well-made brilliants 
almost totally reflect it back toward its source, 
that is, toward -the front of the stone. The well- 



How Rough Stones are Cut 207 

cut diamond is a very brilliant object, viewed 
from the front. 

We must now consider how the "fire" 
or prismatic color play is produced, for it 
is even more upon the display of fire than 
upon its pure white brilliancy that the beauty 
of a^ diamond depends. 

Cause of " Fire." As we saw in Lesson X 
(which it would be well to reread at this time), 
white light that changes its course from one 
transparent medium to another at any but a 
right angle to the surface involved, is not only 
refracted (as we saw in Lesson II) but is dis- 
persed, that is, light of different colors is bent 
by differing amounts and thus we have a separ- 
ation of the various colors. If this takes place 
as the ray of light leaves the upper surface of a 
brilliant the observer upon whose eye the light 
falls will see either the red, or the yellow, or the 
blue, as the case may be, rather than the white 
light which entered the stone. If instead, the 
dispersion takes place as the light enters 



2o8 Precious Stones 

the brilliant the various colored rays thus 
produced will be totally reflected back to 
the observer (slightly weakened by spread- 
ing, as compared to the direct or unreflected 
spectra). Thus dispersion produces the "fire" 
in a brilliant. 

Other materials than diamond behave simi- 
larly, but usually to a much smaller extent, 
for few gem materials have so high a refractive 
power or so great a dispersive power as diamond. 

Having considered the theory of the brilliant 
we may now take up a study of the methods 
by which the exceedingly hard rough diamond 
is shaped and polished. 

Cleaving Diamonds. If the rough material 
is of poor shape, or if it has conspicuous defects 
in it which prevent its being made into a single 
stone, it is cleaved (i. e., split along its grain). 
Hard as it is, diamond splits readily in certain 
definite directions (parallel to any of the tri- 
angular faces of the octahedral crystal). The 
cleaver has to know the grain of rough diamonds 



How Rough Stones are Cut 209 

from the external appearance, even when the 
crystals, as found, are complicated modifica- 
tions of the simple crystal form. He can 
thus take advantage of the cleavage to speedily 
reduce the rough material in size and shape 
to suit the necessity of the case. The cleaving 
is accomplished by making a nick or groove in 
the surface of the rough material at the proper 
point (the stone being held by a tenacious wax, 
in the end of a holder, placed upright in a firm 
support). A thin steel knife blade is then 
inserted in the nick and a sharp light blow 
struck upon the back of the knife blade. The 
diamond then readily splits. 

" Cutting Diamonds." The next step is to 
give the rough material a shape closely similar 
to that of the finished brilliant but rough and 
without facets. This shaping or "cutting" as 
it is technically called, is done by placing the 
rough stone in the end of a holder by means 
of a tough cement and then rotating holder 

and stone in a lathe-like machine. Another 
14 



210 Precious Stones 

rough diamond (sometimes a piece of bort, 
unfit for cutting, and sometimes a piece of 
material of good quality which it is necessary 
to reduce in size or alter in shape) is cemented 
into another holder and held against the surface 
of the rotating diamond. The holder is steadied 
against a firm support. It now becomes a case 
of "diamond cut diamond," each stone wear- 
ing away the other and being worn away itself. 

The cutting process is fairly rapid and it 
leaves the stone (which is reversed to make 
the opposite side) round in form and with a 
rounding top and cone shaped back. Stones 
of fancy shape, such as square, or cushion shape, 
have to be formed in part by hand rubbing or 
"bruting" as it is called. 

The facets must now be polished onto the 
stone. Usually the workers who cut do not 
cleave or polish. 

" Polishing " Diamonds. The polisher fixes 
the cut stone firmly in a metallic holder called a 
dop, which is cleverly designed to hold the stone 



How Rough Stones are Cut 211 

with much of one side of it exposed. The 
holder is then inverted so that the stone is 
beneath and a stout copper wire attached 
to the holder is then clamped firmly in a sort of 
movable vise. The latter is then placed on 
the bench in such a position that the diamond 
resks upon the surface of a rapidly revolving 
horizontal iron wheel or "lap" as it is called. 
The surface of the latter is "charged" with 
diamond dust, that is, diamond dust has been 
pushed into the metal surface which thus acts as 
a support to the dust. The latter wears away 
the diamond, producing a fiat facet. The 
lap is kept moistened with oil and from time to 
time fresh oil and diamond dust are applied. 
A speed of about 2,000 rotations per minute 
is used. 

Facetting. The making of the facets is rather 
slow work, especially when, as is usually the 
case in making the "table" the work has to 
be done against one of the "hard points" 
of the crystal. Great care has to be taken 



212 Precious Stones 

to place the stone so that the grain lies in 
a correct position, for diamond cannot be 
polished against the grain, 'nor even exactly 
with it, but only obliquely across it. This re- 
quirement, as much as anything, has prevented 
the use of machines in polishing diamonds. 
The table is usually first polished on, then the 
four top slopes, dividing the top surface into 
quarters, then each of the four ridges thus 
left, is flattened, making eight facets and 
finally 32 facets, exclusive of the table, are made 
upon the top of the brilliant. The stone is then 
reversed and 24 facets, and the culet, pol- 
ished on the back. As each facet nears its 
proper shape the stone is placed upon a parti- 
cularly smooth part of the lap and a slight 
vibratory motion given to the holder by the 
hand. This smooths out any lines or grooves 
that may have formed because of inequalities of 
surface of the lap. When completely facetted 
the brilliant is finished and requires only to be 
cleaned, when it is ready for sale. 



LESSON XXIII 

HOW ROUGH PRECIOUS STONES ARE CUT AND 

WHAT CONSTITUTES GOOD "MAKE " — Concluded 

Slitting and Cleaving. The cutting and 

polishing of precious stones other than diamond 

is a trade entirely distinct from diamond cutting. 

The precious stone lapidary cuts every species 

of stone except diamond. The methods used by 

different lapidaries vary somewhat in their 

details, and there are many trade secrets which 

are more or less jealously guarded by their 

possessors, but in general the methods used to 

reduce the rough materials to the finished gems 

are as follows: First, the rough material, if of 

too large size, or if very imperfect, is slitted, or, 

if it possesses a pronounced cleavage, it may be 

cleaved, in order to reduce the size or to remove 

imperfect parts. Slitting is accomplished by 
213 



214 Precious Stones 

means of a circular disc of thin metal which is 
hammered so that it will be fiat and rotate 
truly, and is then clamped between face plates, 
much as an emery wheel is held. The smooth 
edge of the circular disc is then charged with 
diamond dust and oil, the diamond dust being 
bedded into the edge of the metal disc by the 
pressure of some hard, fine-grained material, 
such as chalcedony, or rolled into the metal by 
the use of a rotating roller. Once charged, and 
kept freely supplied with oil, a slitting wheel will 
slice a considerable number of pieces of any 
precious stone less hard than diamond, and will 
do so with considerable rapidity. The wheel 
is, of course, rotated very rapidly for this pur- 
pose. 

The Cleaving of certain gem materials, 
such as true topaz (which splits perfectly 
across the prism, parallel to its base) is easily 
accomplished, and it is done in much the same 
manner as the cleaving of diamond. The feld- 
spar gems, such as moonstone, amazonite, and 



How Rough Stones are Cut 215 

labradorite, also cleave very smoothly in certain 
directions. Spodumene, of which Kunzite is a 
variety, cleaves almost too easily to be durable. 
Most gem minerals, however, lack such perfect 
cleavage and when it is desired to remove im- 
perfect parts, or to reduce large pieces to 
smaller sizes, these materials are slitted as above 
described. 

" Rubbing Down." The material being of 
nearly the dimensions of the finished piece, the 
next step is to "rub it down, " as it is called, to 
approximately the shape and size desired. This 
rubbing down process was formerly done by 
means of a soft metal lap (sometimes of lead), 
charged with coarse emery powder and water. 
Carborundum, being harder and sharper than 
emery, has replaced it very largely. Some of the 
softer materials, such, for example, as tur- 
quoise, are rubbed down on a fast flying carbor- 
undum wheel of similar type to those used in 
machine shops for grinding steel tools. These 
wheels rotate in a vertical plane and are kept 



2i6 Precious Stones 

wet. The laps before mentioned run hori- 
zontally. The carborundum wheels have the 
grains of carborundum cemented together by 
means of some binding material and this gradu- 
ally crumbles, exposing fresh, sharp cutting 
edges. Various sizes of grain, and various 
degrees of hardness of the binding material, as 
well as various speeds, are needed to suit the 
many different materials rubbed down by the 
lapidary. Some lapidaries rub down the harder 
and more valuable gems such as ruby upon 
diamond charged laps of brass or other metal. 
Cabochons. The rubbing down process does 
not leave a facetted surface, but only a coarse 
roughly rounded or flattened surface. If the 
material is to be left in some one of the fiat- 
backed, rounded top forms known as cabochon 
cut, the surfaces need only to be smoothed (by 
means of very fine abrasives such as fine emery 
applied by means of laps, or even by fine emery 
or carborundum cloth), and they are then 
ready for polishing. 



How Rough Stones are Cut 217 

Facetted Stones. If, however, the stone 
is to be facetted in either the brilliant form, 
somewhat like the diamond, or step cut or 
otherwise facetted, it is cemented strongly 
onto a holder (much like the wooden part 
of a pen holder). The upper end of the holder 
is jrested in one of a series of holes in what is 
called a " ginpeg'^ resting in the work-bench 
near a metal lap, and the stone is pressed upon 
the rapidly rotating surface of the lap, which is 
charged with diamond dust or carborundum, 
according to the hardness of the material to be 
facetted. A fiat facet is thus ground upon the 
stone. By rotating the holder a series of facets, 
all in the same set, is produced. The holder is 
then changed to a new position on the ginpeg and 
another set of facets laid upon the stone. Thus 
as many as four or five tiers or sets of facets may 
be applied to one side, say the top of the stone. 
The latter is then removed, from the holder and 
cemented to it again, this time with the bottom 
exposed, and several sets of facets applied. 



2i8 Precious Stones 

The stone is now cut but not polished. The 
facets are flat, but have a rough ground-glass 
like surface. The polishing is usually done by 
workers who do not cut stones, but who do 
nothing but polish them. In small shops, how- 
ever, the same lapidary performs all the parts 
of the work. 

Polishing. The polishing of stones, whether 
cabochon or facetted, is accomplished by the 
use of very finely powdered abrasives such 
as corundum powder, tripoli, pumice, putty 
powder, etc. Each gem material requires 
special treatment to obtain the best results. 
It is here that most of the trade secrets apply. 

The troubles of the lapidary in getting the 
keen polish that is so much admired on fine 
gems are many. In general, the polishing pow- 
der should not be quite as hard as the material 
to be polished, else it may grind rather than 
polish. The material should be used with water 
or oil to give it a creamy consistency. It should 
be backed by laps of different materials for 



How Rough Stones are Cut 219 

different purposes. Thus, when backed by a 
fairly hard metal even tripoli, although much 
softer, will polish sapphire. On a lap of wood, 
tripoli would fail to polish hard materials, but 
Would polish amethyst or other quartz gem. A 
change of speed of the lap, too, changes the 
effopt of the polishing material. I have seen a 
lapidary, who was having no success at pol- 
ishing an emerald, get very good results by using 
a stick as a brake and slowing down his lap. 

The polishing material must be of very 
uniform size, preferably water floated or oil 
floated, to give good results. The lap must be 
kept flat and true and the stone must be properly 
held, or the flatness of the facets, upon which 
brilliancy depends in part, will be destroyed 
during the polishing. 

The softer materials, such as opal, require 
treatment more like that accorded cut glass, 
and soft abrasive powders, such as pumice, 
suffice to polish them. Probably hardly two 
lapidaries would work exactly alike in their 



220 Precious Stones 

treatment of precious stones, and each guards 
his secrets, yet all use approximately similar 
general methods. Some have devised mechani- 
cal holders which permit the repeated cutting of 
stones to exactly the same angles, and that, too, 
with an accurate knowledge of the angles 
used. These angles can be definitely altered 
for different materials, according to their 
refractive indices. Other lapidaries produce 
very fine results by purely hand methods. 

These details have been gone into to give 
an idea of the methods of the lapidary and of 
the many variations in method. In general, 
however, the slitting or cleaving, the rubbing 
down to shape, the* smoothing out of all scratches 
and the facetting and polishing are done some- 
what similarly by all lapidaries. 

Having now had a glimpse of the meth- 
ods of the lapidaries, let us briefly consider 
what constitutes good "make" in stones other 
than diamond. 

Good " Make " in Colored Stones. Bril- 



How Rough Stones are Cut 221 

Hants, cut from materials having smaller refrac- 
tive indices than diamond, (and this group 
includes nearly all stones other than diamonds) 
should have steeper back angles and higher 
tops than the best diamond brilliants have. A 
3 5 -degree top angle (the angle between the slope 
of ihe top and the plane of the girdle is called 
the top angle) and a 41 -degree back angle 
being about ideal for diamond, other gem 
materials should have more nearly a 39-degree 
top angle and a 44-degree back angle to give 
the greatest possible brilliancy. However, in 
the case of colored gems such as ruby, sapphire, 
etc., where the value depends even more largely 
upon the color than upon the brilliancy, it is 
frequently necessary to cut the brilliant thicker 
or thinner than these proportions in order to 
deepen or to thin the color. 

In general, the thicker a stone of a given 
spread the deeper the color will be. The 
color may also be deepened by giving to the 
stone a rounded contour, both above and below 



222 Precious Stones 

the girdle, and facetting it in steps instead of in 
the brilliant form. Increasing the number of 
steps also serves to slightly deepen the color, as a 
larger number of reflections is thus obtained 
within the material, the light thus has to 
travel a greater distance through the col- 
ored mass, and more of the light, of color 
other than that of the stone, is absorbed. 

Improving Color by Proper Cutting. In 
addition to the color improvement that can be 
brought about by changing the shape of the cut 
stone there are a number of gem materials whose 
color varies very greatly in different directions, 
and this fact calls for skillful use in order to 
obtain the best possible results. Thus most 
tourmalines of deep color must be cut with the 
top or table, of the finished stone, on the side 
of the prismatic crystal rather than at right 
angles to the axis of the prism. If cut the 
latter way they would be much too dense in 
color. On the other hand, most blue sapphires 
should be cut across the prism axis rather than 



How Rough Stones are Cut 223 

the way that tourmalines should be cut. To 
cut a sapphire with its table on the side of the 
prism would be likely to cause it to have a 
greenish cast because of the admixture of the 
unpleasing "ordinary ray" of yellowish tint 
with the blue of the stone as seen up and down 
the^rism. Some Australian sapphires are of 
a pronounced green when viewed across the 
axis of the crystal. 

Rubies if cut, as was recommended for 
sapphires, give a very pure and very deep red 
color, but lack somewhat in the display of 
dichroism given by rubies that are cut with 
the table on the side of the crystal and parallel 
to its axis. Lapidaries need to know and to 
make use of such optical relations as these and 
jewelers might well inform themselves in such 
matters, especially if they have, or hope to 
acquire, trade in very fine colored stones. 

Effect of Shape on Brilliancy. In actual 
practice it is common to find colored stones 
poorly cut for brilliancy, especially central 



224 Precious Stones 

brilliancy, and that, too, without the excuse of 
sacrifice of brilliancy in order to improve 
color. The fault is usually due to too great a 
desire to save size and weight. Frequently a 
stone would have greater value if properly cut, 
even at the expense of some size and weight. 
When stones are cut too shallow, as is frequently 
the case, they are sure to leak light in the center 
and they are thus weak and less brilliant there 
than they would be if made smaller in diameter 
and with steeper back slopes approximating 44 
degrees. 

Round stones, if their angles are correct, are 
more brilliant than stones of other contour such 
as square or cushion shape, or navette or heart 
shape. It can readily be seen that such odd 
shaped stones can hardly have the same top and 
back angles at every part of their circumference. 
If the angle from a corner of a square stone is 
correct then the angle from the middle of one 
side is obviously a little different. Small differ- 
ences of angle make considerable differences in 



How Rough Stones are Cut 225 

the brilliancy of cut stones. The prevailing 
tendency to cut nearly all diamonds round 
depends largely upon the above facts. In the 
case of colored stones, however, the added at- 
tractiveness which comes with odd or different 
contour more than makes up for the slight loss 
of brilliancy'' that may attend upon the shape 
selected. Such shapes as lend themselves 
to special designs in mountings also justify 
any little loss in brilliancy that accompanies 
the change in shape, provided the proportions 
retained give a considerable amount of total 
reflection within the stone and thus light up 
most of the stone as seen from the front. 

The test of the "make" of a color stone 
is its appearance. If it lights up well over most 
of its surface and if the color is right, one should 
not criticize the "make" as one would be justi- 
fied in doing in the case of a diamond. If, how- 
ever, the effect is less attractive it would many 
times be advisable to measure the angles 

of the stone, or its thickness and spread as 
15 



226 Precious Stones 

compared with similar measurements on a stone 
of fine appearance. Frequently one will thus 
find the reason for the failure of the stone to per- 
form as it might, and recutting should be resort- 
ed to in such cases in order to get a smaller but 
more beautiful and hence more valuable stone. 



LESSON XXIV 

FORMS GIVEN TO PRECIOUS STONES 

"\ \/HILE precious stones are cut to many 
different forms, there are, neverthe- 
less, but a few general types of cutting. These 
may be classified as follows: First, the "cabo- 
chon'* (Fig. ii) type of cutting; second, the old 
"rose^^ (Fig. 12) type of cutting; third, the 
brilliant (Fig. 13) ; fourth, the step cutting (Fig. 

14). 

Cabochons. Of these the first, or cabochon 
cutting, is probably the most ancient. The 
term comes from a French word signifying 
a bald pate (caboch, from Latin cabo, a head). 
The usual round cabochon cut closely resembles 
the top of a head in shape. Cabochon cut 
stones usually have a flat base, but sometimes a 

slightly convex base is used, especially in opals 

227 



228 Precious Stones 

and in moonstones, and some stones of very 
dense color are cut with a concave base to thin 
them and thus to reduce their color. The con- 
tour of the base may be round, or oval, or square, 
or cushion shape, or heart shape or of any regu- 
lar form. The top is always smooth and 




C") (bj M 

fro>ii eMaiion ^^ Jrcnt Cki/aiiao 

Fig. 11. — CABocHON cutting. 



rounding and unfacetted. The relation of 
the height or thickness to the length or width 
may be varied to suit the size and shape of the 
rough piece or to suit one's ideas of symmetry, 
provided the material be an opaque one, such as 
turquoise or lapis lazuli. If, however, the 
material is transparent the best results in the 
way of the return of light to the front, and hence 
in the display of the color of the material, are 
had if the thickness is about one half the spread. 



Forms Given to Precious Stones 229 

This relation depends upon the refrac- 
tive index of the material, but as most color 
stones are of somewhat similar refractive indices, 
the above proportions are sufficiently accurate 
for all. The object in view is the securing of 
total reflection of as much light as possible 
from the fiat polished back of the stone. Cabo- 
chon stones are sometimes set over foil or on 
polished gold to increase the reflection of 
light. 

The path of a ray of light through a cabochon 
cut stone is closely similar to that through a rose 
cut diamond [see cut (c) of Fig. 12 for the latter.] 
Like the rose cut, the cabochon cut does not 
give much brilliancy as compared to the bril- 
liant cut. Cabochon cut stones, however, 
have a quiet beauty of color which commends 
them to people of quiet taste, and even fine 
rubies, sapphires, and emeralds are increasingly 
cut cabochon to satisfy the growing demand 
for fine taste in jewels. The East Indian has 
all along preferred the cabochon cut for color 



230 Precious Stones 

stones, but possibly his motives have not 
been unmixed, as the cabochon cut saves 
a greater^proportion of the weight of the rough 
stone than the more modern types of cutting. 

Garnets, more than other stones, have 
been used in the cabochon cut, and when 






(c) 
Fig. 12 — rose cutting. 



in that form are usually known as carbuncles 
(from carbunculus, a glowing coal) . Any other 
fiery red stone might equally well be styled a 
carbuncle, especially if cabochon cut. 

Scientific rubies look very well in the cabo- 
chon cut. 

Fig. II shows in (a) and (b) the front and 
top of the usual round cabochon. Cut (c) 
of the same figure gives the front elevation of a 
cabochon which will light up better than the 



Forms Given to Precious Stones 231 

usual round topped design. In the round 
topped type the central part of the top is so 
nearly parallel to the back that light can pass 
right through as through a window pane. If the 
sloping sides are brought up to a blunt point, as 
in cut (c) there is very much less loss of light 





(a) 

Jrmt eieVaUon 

Fig. 13 — brilxiant cutting 

and greater beauty results. The East Indian 
cabochons are frequently cut in a fashion resem- 
bling that suggested. 

Rose Cut Stones. It was natural that the 
earliest cut stones should have the simple 
rounded lines of the cabochon cutting, for the 
first thing that would occur to the primitive 
worker who aspired to improve upon nature's 
product, would be the rubbing down of sharp 
edges and the polishing of the whole surface of 



232 Precious Stones 

the stone. Perhaps the next improvement was 
the polishing of flat facets upon the rounded 
top of a cabochon stone. This process gives 
us the ancient type of cutting known as the 
rose cut. The drawings (a) and (b) of Fig. 12 
show the front elevation and the top and (c) 
shows the path of a ray of light through a "rose," 
It will be noted that the general shape resembles 
that of a round cabochon, but twenty-four tri- 
angular facets have been formed upon the top. 
The well-proportioned rose has a thickness about 
one half as great as its diameter. Diamonds 
were formerly cut chiefly in the rose form, 
especially in the days of the East Indian mines, 
and even in the early part of the nineteenth 
century many people preferred finely made 
roses to the thick, clumsy brilliants of that day. 
To-day only very small pieces of diamond 
are cut to "roses." As the material so used 
frequently results from the cleaving of larger 
diamonds, the public has come to know these 
tiny roses as "chips." 



Forms Given to Precious Stones 233 

The best roses have twenty-four regular facets 
but small ones frequently receive only twelve, 
and those are seldom regular in shape and in 
arrangement. Such roses serve well enough 
for encrusting watch cases and for similar work, 
as the flat base of the stone can be set in thin 



l<^^ 




(a) 

front 6Ui}atiot 



k^ 



(b) 



(9) 
Back 



Fig. 14 — step cutting. 



metal without difficulty. About the only gem 
other than diamond that is now cut to the 
rose form is garnet. Large numbers of small 
Bohemian garnets are cut to crude rose form 
for use in cluster work. 

The brilliant cut, as its name implies, gives 
the most complete return of light of any of 
the forms of cutting. The theory of the bril- 
liant has already been discussed (Lesson XXII. 
in connection with the cutting of diamond) . The 



234 Precious Stones 

shape of the brilliant is too well known to require 
much description. Most brilliants to-day are 
cut practically round and the form is that of two 
truncated cones placed base to base. The upper 
cone is truncated more than the lower, thus form- 
ing the large, fiat top facet known as the table of 
the stone [A, Fig. 13, cut (a)]. The truncating 
of the lower cone forms the tiny facet known as 
the culet, which lies opposite to the table and 
is parallel to the latter [see B, Fig. 13, cut (a)]. 
The edge of meeting of the two cones is the 
girdle of the brilliant [CD in cut (a). Fig. 13]. 
The sloping surface of the upper cone is facetted 
with thirty-two facets in the full cut brilliant, 
while the lower cone receives twenty-four. 

Small stones sometimes receive fewer facets, 
to lessen the cost and difficulty of cutting, 
but by paying sufficient for them full cut bril- 
liants as small as one hundred to the carat may 
be had. Cut (b) of Fig. 13 shows the proper 
arrangement of the top facets and cut (c) that 
of the bottoin facets. 



Forms Given to Precious Stones 235 

When cutting colored stones in the bril- 
Hant cut, especially if the material is very- 
costly and its color in need of being dark- 
ened or lightened, the lapidary frequently 
takes liberties with the regular arrangement 
and proportions depicted in the cuts. 

Step Cutting. The only remaining type of 
cutting that is in very general use is the step cut 
(sometimes known as trap cut). Fig. 14, 
(a), (b), and (c), shows the front elevation, the 
top and the back of a square antique step cut 
stone. The contour may be round or complete- 
ly square or oblong or of some other shape, just 
as a brilliant may have any of these contours. 
The distinctive feature of the step cutting is the 
several series of parallel-edged quadrangular 
facets above and below the girdle and the 
generally rounding character of its cross section. 
This plump, rounding character permits the sav- 
ing of weight of the rough material, and by mass- 
ing the color gives usually a greater depth of 
color than a brilliant of the same spread would 



236 Precious Stones 

have if cut from similar material. While prob- 
ably never quite as snappy and brilliant as the 
regular brilliant cut, a well-proportioned step 
cut stone can be very brilliant. Many fine 
diamonds have recently been cut in steps for use 
in exclusive jewelry. 

The Mixed Cut. The ruby and the emerald 
are never better in color than when in the full 
step cut, although rubies are frequently cut in 
what is known as the mixed cut, consisting of 
a brilliant cut top and a step cut back. Sap- 
phires and many other colored stones are 
commonly cut in the mixed cut. Recently it 
has become common to polish the tops of col- 
ored stones with a smooth unfacetted, slightly 
convex surface, the back being facetted in 
either the brilliant or the step arrangement. 
Such stones are said to have a ''buffed top.** 
They are less expensive to cut than fully facetted 
stones and do not have the snappy brilliancy 
of the latter. They do, however, show off the 
intrinsic color of the material very well. 



LESSON XXV 

imitations' OF PRECIOUS STONES 

"J*aste" Gems, Large volumes have been 
written on paste jewels, especially on antique 
pastes. Contrary to a prevailing belief, the 
paste gem is not a recent invention. People 
frequently say when told that their gems 
are false, "But it is a very old piece, it must be 
genuine." The great age of a jewel should 
rather lead to suspicion that it was not genuine 
than give confidence that a true gem was 
assured. The Egyptians and Romans were 
skillful makers of glass of the sort used in 
imitating gems and some of the old pastes were 
very hard or else have become so with age. 

Glass of one variety or another makes the 
most convincing sort of imitation precious 

stones. The term "paste" as applied to glass 

237 



238 Precious Stones 

imitations is said to come from the Italian 
pasta meaning dough, and it suggests the soft- 
ness of the material. Most pastes are mainly- 
lead glass. As we saw in Lesson XVIII., on the 
chemical composition of the gems, many of them 
are silicates of metals. Now glasses are also 
silicates of various metals, but unlike gem 
minerals the glasses are not crystalline but 
rather amorphous, that is, without definite 
geometric form or definite internal arrangement. 

The optical properties of the various glasses 
vary chiefly with their densities, and the denser 
the material the higher the refractive index 
and the greater the dispersion. Thus to get the 
best results in imitation stones they should be 
made of very heavy glass. The dense flint glass 
(chiefly a silicate of potassium and lead) which is 
used for cut glass ware illustrates admirably 
the optical properties of the heavy glasses. 
By using even more lead a still denser glass may 
be had, with even a greater brilliancy. 

Unfortunately the addition of lead or other 



Imitations of Precious Stones 239 

heavy metals (such as thallium) makes the 
product very soft and also very subject to attack 
by gases such as are always present in the 
atmosphere of cities. This softness causes 
the stones to scratch readily so that when worn 
they soon lose their polish and with the loss of 
poli§h they lose their beauty. The attack of the 
gases before mentioned darkens the surfaces 
of the imitation and further dulls it. When 
fresh and new a well cut piece of colorless 
paste has a snap and fire that approaches 
that of diamond. The surface luster is not 
adamantine, however, and the edges of the 
facets cannot be polished so sharply as those 
on a diamond. Moreover the refractive index, 
while high, is never so high as in a diamond 
and hence the brilliant cannot be so shaped 
as to secure the amount of total reflection given 
by a well-made diamond. Hence, the paste 
brilliant, while quite satisfying as seen from 
squarely in front, is weak and dark in the center 
as seen when tilted to one side. By these differ- 



240 Precious Stones 

ences the trained eye can detect paste imi- 
tations of diamond at a glance without recourse 
to tests of specific gravity, hardness, etc. 

Pastes, being amorphous, are singly re- 
fracting, as is diamond. This fact helps 
the appearance of the paste brilliant, for light 
does not divide within it to become weakened 
in power. This singleness of refraction, how- 
ever, betrays the paste imitation when it is 
colored to resemble ruby, sapphire or emerald, 
all of which are doubly refracting. 

The color is imparted to pastes by the 
addition, during their manufacture, of vari- 
ous metallic oxides in small proportions. Thus 
cobalt gives a blue color, copper or chromium 
green, copper or gold give red (under proper 
treatment) and manganese gives purple. By 
experiment the makers of pastes have become 
very skillful in imitating the color of almost 
any precious stone. Fine paste emeralds may 
look better than inferior genuine emeralds. 

As pastes are singly refracting and hence 



Imitations of Precious Stones 241 

lack dichroism, the pleasing variety of color 
of the true ruby cannot be had in a paste 
imitation, but the public is not critical enough 
to notice this lack. The expert would, however, 
note it and could detect the imitation by that 
difference as well as by the lack of double 
refraction. The use of direct sunlight and a 
white card as already explained in the lesson 
on double refraction (Lesson III.) will serve to 
expose the singleness of refraction of paste 
imitations. Spinels and garnets are about the 
only true gems (except diamond) that are 
single refracting. Any other color stone should 
show double refraction when tested by the sun- 
light-card method. The file test will also 
expose any paste imitation as all the very 
brilliant pastes are fairly soft. 

Doublets. To give better wearing quality to 
paste imitations the doublet was devised. This 
name is used because the product is in two 
parts, a lower or back portion of paste and 

an upper or top portion of some cheap but 
16 



242 Precious Stones 

hard genuine stone. Garnet is probably used 
for this purpose to a greater extent than any- 
other material, although quartz or colorless 
topaz will do very well. 

The usual arrangement of the parts can 
be seen in Fig. 15, the garnet covering only 




Fig 15. one form of cheap doublet., 

a part of the upper surface, namely the table 
part and a small portion of the sloping surface 
of the top. In high class doublets the hard 
mineral covers the paste to the girdle. (See 
Fig. 16.) The color of the garnet does not 
interfere seriously with that of the paste. 

If a "diamond" doublet is desired the 
slice of garnet is made nearly as thin as paper 
and it covers only the table of the brilliant. It 
is thus practically colorless. A thin slice of red 



Imitations of Precious Stones 243 

garnet over a green background is not notice- 
able, as all the red is absorbed in passing 
through the green material beneath. With a 
blue base, the red upper layer may give a 
very slight purple effect. With yellow a 
slight orange tint results and of course with 



G/f/SN£T 




,FlG- 16. ANOTHER FORM OF DOUBLET.. 

a red back no perceptible difference would 
result. 

The two materials are cemented together, 
by means of a transparent waterproof cement. 
The triplet has already been described in Lesson 
XII. It is even better than the doublet and 
more difficult to detect. Both the file test and 
the sunlight-card test serve to detect doublets, 
as well as paste imitations, except that in the file 
test with the fully protected doublet the hack of 



244 Precious Stones 

the stone must be tested with the file, as the 
girdle and top are of hard material. 

In the sunlight-card test of a doublet (the 
refraction of garnet being single like that of 
glass), single images of the facets will be had on 
the card when the sunlight is reflected onto 
it. A reflection of the lower or inner surface 
of the garnet top can be seen also and this 
serves to still further identify a doublet or 
a triplet. The appearance of this reflection 
is much like that received on the card from 
the top of the table. It is larger than the 
reflections of the smaller facets and is but 
little colored. 

Tests for Doublets. A trained eye can also 
detect a doublet or a triplet by noting the 
difference in the character of the surface luster 
of the garnet part and of the glass part. Garnet 
takes a keener and more resinous luster than 
glass. By tipping the doublet so that light is 
reflected to the eye from the sloping top sur- 
face, one can see at once where the garnet 



Imitations of Precious Stones 245 

leaves off and the glass begins. Even through 
a show window one can tell a doublet in this way 
although here it is necessary to move one- 
self, instead of the stone, until a proper position 
is obtained to get a reflection from the top slope 
of the doublet. 

It the garnet covers the whole top of the 
imitation then it is not possible to get so direct 
a comparison, but even here one can look first 
at the top surface and then at the back and thus 
compare the luster. It is also well to closely 
examine with a lens the region of the girdle, to 
see if any evidence of the joining of two ma- 
terials can be seen. Frequently the lapidary 
bevels the edge so as to bring the line of junc- 
tion between real and false material at the sharp 
edge of the bevel. Boiling a doublet in alcohol or 
chloroform will frequently dissolve the cement 
and separate the parts. 

The dichroscope also serves to detect the 
false character of doublets and paste imita- 
tions, as neither shows dichroism. As rubies, 



246 Precious Stones 

emeralds, sapphires, and in fact most colored 
stones of value, show distinct dichroism, this 
test is a sure one against these imitations. 

Triplets and doublets too may be exposed by- 
dipping them sidewise into oil, thus removing 
the prismatic refraction almost completely, as the 
oil has about the same refractive index as the 
stone. One can then look directly through 
glass and garnet, or other topping material, 
separately, and each material then shows its 
proper color. Thus zones of color appear in 
a doublet or triplet when under the oil. A 
real gem would appear almost uniform in color 
under these conditions. 

Round gas bubbles can frequently be found 
in paste, and hence in the paste part of a doub- 
let. Also, the natural flaws of the real stone are 
never found in paste, but may be present in the 
real stone part of a doublet or a triplet. Some 
imitation emeralds on the market, however, 
have been made in a way to counterfeit the 
flaws and faults generally found in this stone. 



Imitations of Precious Stones 247 

Altered Stones. In addition to the out and 
out imitations made of paste, and the doublets, 
there are numerous imitations current in the 
trade that are made by staining or by otherwise 
altering the color of some genuine but inexpen- 
sive gem material. 

P]pr example, large quantities of some- 
what porous chalcedony from Brazil are stained 
and sold in imitation of natural agate or sard 
or other stones. In many cases the staining 
is superficial, so that the stone has to be 
shaped before it is stained, then stained and 
polished. 

Large quantities of slightly crackled quartz 
are stained to resemble lapis lazuli, and sold, 
usually with the title "Swiss Lapis." A file 
test will reveal the character of this imitation, 
as it is harder than a file, while true lapis is 
softer. The color too is never of so fine a blue 
as that of fine lapis. It has a Prussian blue 
effect. 

Turquoises of inferior color are also some- 



248 Precious Stones 

times stained to improve them. A better 
product is made artificially. 

Opals are sometimes impregnated with or- 
ganic matter, which is then charred, perhaps 
with sulphuric acid, thus giving them some- 
what the appearance of black opal. 

Opals are also imitated by adding oxide 
of tin to glass, thus imparting a slight milkiness 
to it. The imitation is then shaped from this 
glass by molding, and the back of the cabochon 
is given an irregular surface, which may be set 
over tinsel to give the effect of "fire. " 

Pale stones are frequently mounted over 
foil, or in enameled or stained settings and 
thus their color is seemingly improved. 

Diamonds of poor color are occasionally 
"painted"; often the back of the brilliant is 
treated with a violet dyestuff, which even in 
so small an amount that it is difficult to detect, 
will neutralize the yellow of the stone and make 
it appear to be of a fine blue-white color. The 
"painting" is, of course, not permanent, so 



Imitations of Precious Stones 249 

that such treatment of a diamond with a view 
to selling it is fraudulent. The painted stone 
may be detected by washing it with alcohol, 
when the dye will be removed and the off-color 
will become apparent. If the stone is unset 
one can see with a lens a wavery metallic 
appearance on the surfaces that have been 
"painted." This effect is due to the action 
of the very thin film of dye upon the light that 
falls upon it. 

Besides the staining of genuine materials, 
they are sometimes altered in color by heat 
treatment, and this topic will be discussed 
in the next lesson. 



LESSON XXVI 

ALTERATION OF THE COLOR OF PRECIOUS STONES 

/V/TANY gem minerals change color when 
more or less strongly heated. Extreme 
heat whitens many colored materials com- 
pletely. 

" Pinked Topaz. " John Ruskin advises us 
to "seek out and cast aside all manner of false 
or dyed or altered stones" but, in spite of his 
advice, perhaps the most justifiable use of heat 
treatment is that which alters the color of 
true topaz from a wine-yellow to a fine pink. 
It would appear that the wine-yellow is a com- 
posite color composed of pink and yellow and 
that the pink constituent is less easily changed 
by heat than is the yellow one. If too high a 
temperature is used both colors disappear and 

white topaz results. As the latter is abundant 
250 



Alteration of the Color 251 

in nature and of little value, such a result is very- 
undesirable. Pink topaz, however, is very 
rare, and until recently, when pink tourmaline 
from California and Madagascar, and pink 
beryl (morganite) from Madagascar, became 
available in quantity, the "pinked " topazes 
hackbut few competing gems, and thus com- 
manded a higher price than the natural topazes. 
Of course, care has to be taken in heating a 
mineral to raise and lower the temperature 
slowly, in order to avoid sudden and unequal 
expansion or contraction, which would crack 
and ruin the specimen, as the writer learned to 
his sorrow with the first topaz that he tried to 
"pink." 

Spanish Topaz. Another material that gains 
a more valuable color by heat treatment is the 
smoky quartz of Spain, which, on being gently 
heated, yields the so-called Spanish topaz. 
Some amethysts are altered to a yellow color 
by mild heating. Too great a temperature 
completely decolorizes colored quartz. Some 



252 Precious Stones 

dark quartz yields a nearly garnet red product, 
after heating. 

Zircon. Slight increase in temperature 
causes many of the zircons from Ceylon to 
change markedly in color. An alcohol flame 
serves admirably to effect the change, care 
being taken to warm up the stone very gradu- 
ally and to cool it slowly. Drafts should be 
prevented, as they might suddenly cool the 
stone and crack it. Some zircons become 
completely whitened by this treatment. At 
the same time they increase markedly in density 
and in refractive index and thus become even 
m.ore snappy and brilliant than when colored. 
One is tempted to suspect that the "space 
lattice" of the crystal has had its strata drawn 
closer together during the heating and left 
permanently in a closer order of arrangement. 
Other zircons merely become lighter colored 
and less attractive. Some of the whitened 
stones again become more or less colored on 
exposure to strong light. Ultra-violet light 



Alteration of the Color 253 

will sometimes restore these to a fine deep color 
in a short time. 

The whitened zircon, when finely cut in the 
brilliant form, with truly flat facets and sharp 
edges and with a top angle of about 39 degrees 
and a back angle of about 44 degrees, so closely 
resgpibles a diamond that it will deceive almost 
anyone on casual inspection. The expert, even, 
may be deceived, if caught off his guard. The 
writer has a fine specimen of a little over one 
carat, with which he has deceived many jewelers 
and pawnbrokers, and even an importer or 
two. If it is presented as a stone that closely 
resembles diamond your expert will say: "Yes, 
it is pretty good, but it would never fool me. " 
If, however, you catch him off his guard by 
suggesting, perhaps, "Did you ever see a dia- 
mond with a polished girdle? ", then he will look 
at it with interest, remark on its fine color and 
"make," and never think of challenging its 
character. 

The refractive index of the dense type 



254 Precious Stones 

of zircon is so high (1.92- 1.98) that it Hghts up 
well over most of the surface of the brilliant 
when cut, as above indicated, and does not 
show markedly the weak dark center shown by 
white sapphire, white topaz, colorless quartz, 
colorless beryl, and paste, when seen from the 
side. Moreover, the luster of zircon is nearly 
adamantine, so the expert does not miss the cold 
metallic glitter as he would with any other 
white stone. The color dispersion, too, is 
so high (86% as great as in diamond) that the 
zircon has considerable "fire," and thus the 
casual handler is again deceived. A fine white 
zircon is really prettier than a poor diamond. 
It cannot compare, however, with a fine dia- 
mond. It would never do to let an expert see 
your zircon beside even a fair diamond. The 
zircon would look " sleepy. " It is only when no 
direct comparison is possible, and when the 
expert is not suspicious, that a zircon- can 
deceive him. Of course, the use of the scien- 
tific tests of the earlier lessons will, at once, 



Alteration of the Color 255 

detect the character of a whitened zircon. The 
hardness is but 7.5, the refraction so strongly 
double that the edges of the back facets appear 
double-lined when viewed through the table 
with a lens, and the specific gravity is 4.69. 
Double spots of light appear on the card when 
the sunlight-card test is applied. Hence, it is 
easy to detect zircon by any of these tests 
if there is reason to suspect that it has been 
substituted for diamond. 

Corundum Gems. Rubies of streaky color 
are said to be improved by careful heating. 
Usually ruby undergoes a series of color changes 
on being heated, but returns through the same 
series in reverse order on being, cooled, and 
finally resumes its original color. Strong heat- 
ing will whiten some yellow sapphire. The 
author thus obtained a white sapphire from a 
crystal of light yellow material. 

It is interesting to note that the corun- 
dum gems undergo marked change in color 
under the influence of radium. A regular 



256 Precious Stones 

series of changes is said to be produced in 
white sapphire by this means, the final color 
being yellow. This color may then be re- 
moved by heat and the series run through 
again. It is not stated that a fine red has 
ever been thus obtained. Perhaps Nature, 
by her slower methods, using the faint traces 
of radio-active material in the rocks, reddens 
the corundum of Burmah at her leisure, and 
finally arrives at the much sought "pigeon 
blood" color. It is said that the natives of 
India have a legend to the effect that the white 
sapphires of the mines are "ripening rubies," 
and that one day they will mature. Perhaps 
they are not far wrong. 

Diamond. Diamonds of yellowish tint may 
be improved in color by the use of high-power 
radium. At present the latter is so rare and 
costly that there is no evidence of its commercial 
use for this purpose. Scientists have brought 
about the change to a light blue as an experi- 
ment. It is not yet known whether the change 



Alteration of the Color 257 

will be permanent. Perhaps here again Nature 
has anticipated man's discovery and made the 
fine bluish-violet Brazilian diamonds (which 
fluoresce to a deep violet under an arc light, 
and which shine for a few moments in the dark 
after exposure to light) by associating them for 
ages with radio-active material. Some of the 
African stones also have these characteristics. 
Aside from the change in the color of diamond 
that may be brought about by means of radium, 
the mineral is extremely reluctant to alter its 
color. Many experimenters besides the author 
have tried in vain a host of expedients in the 
hope of finding some way to improve the color of 
diamond. About the only noticeable alter- 
ation that the author has been able to bring 
about was upon a brown diamond, the color 
of which was made somewhat lighter and more 
ashen by heating it in a current of hydrogen 

gas to a low red heat. 
17 



LESSON XXVII 



PEARLS 



r TNLIKE the gems that have been so far 
considered, the pearl is not a mineral, 
but is of organic origin, that is, it is the product 
of a living organism. There are two principal 
types of molluscs which yield true pearls in 
commercial quantities. The best known of 
the first type is the so-called pearl oyster 
{meleagrina margaritifera) . The pearl mussel 
of fresh water streams is of the second type 
{uniomargarifer) . Other species of molluscs 
having pearly linings to their shells may produce 
pearls, but most of the pearls of commerce come 
from one or the other of the two varieties 
mentioned. 

Structure of Pearl. The structure and mate- 
rial of the true pearl must be first understood 
258 



Pearls 259 

in order to understand the underlying reasons 
for the remarkable beauty of this gem. Pearls 
are composed partly of the mineral substance 
calcium carbonate (chemically the same as 
marble) and partly of a tough, horny sub- 
stance of organic nature called conchiolin. 
Tt|^ shell of the pearl-bearing mollusc is also 
composed of these two substances. Calcium 
carbonate may crystallize in either of two forms, 
calcite or aragonite. In marble we have cal- 
cite. In the outer portions of the shell of the 
pearl oyster the calcium carbonate is in the form 
of calcite, but in the inner nacreous lining and in 
the pearl itself the mineral is present as ara- 
gonite. This is deposited by the mollusc 
in very thin crystalline layers in the horny 
layers of conchiolin, so that the lining of the 
shell is built of approximately parallel layers 
of mineral and of animal substance. In the 
normal shell this is all that takes place, but in 
the case of a mollusc whose interior is invaded 
by any small source of irritation, such as a borer, 



26o Precious Stones 

or a grain of sand, or other bit of foreign mate- 
rial, a process of alternate deposit of conchiolin 
and of aragonite goes on upon the invading 
matter, thus forming a pearl. 

The pearl is built in layers like an onion. In 
shape it may be spherical, or pear shaped, or 
button shaped or of any less regular shape 
than these. The regular shapes are more 
highly valued. The spherical shape is of great- 
est value, other things being equal. Next 
comes the drop or pear shape, then the button 
shape, and after these the host of irregular shapes 
known to the jeweler as "baroques." The 
river man who gathers mussels calls these odd 
shaped pearls "slugs." 

Let us now attempt to understand how the 
beautiful luster and iridescence of the pearl 
are related to the layer-like structure of the gem. 
In the first place, it should be understood 
that both conchiolin and aragonite are translu- 
cent, that is, they pass light to a certain extent. 
The layers being exceedingly thin, light can 



Pearls 261 

penetrate a considerable number of them if not 
otherwise deflected from its course. We thus 
obtain reflections not merely from the outer sur- 
face of a pearl, but from layer after layer 
within the gem and all these reflections reach 
the eye in a blended reflection of great beauty. 
Thp luster of a pearl is then not purely a surface 
luster in the usual sense of that term, but it is a 
luster due to many superposed surfaces. It is 
so different from other types of luster that we 
describe it merely as pearly luster even though 
we find it in some other material, as, for example 
in certain sapphires, in which it is due to a 
similar layer-like arrangement of structure. 

Orient. The fineness of the luster of a pearl, 
or as is said in the trade, the orient, depends 
upon the number of layers that take part 
in the reflection, and this number in turn 
depends upon the translucency of the ma- 
terial and the thinness of the layers. Very 
fine pearls usually have very many, very 
thin layers taking part in the reflection. The 



262 Precious Stones 

degree of translucency, considered apart, is 
sometimes called the "water" of the 
pearl. 

In addition to their beautiful luster, many- 
pearls display iridescence, and this is due in 
part, as in the case of the pearly lining of the 
shell (mother of pearl) to overlapping of suc- 
cessive layers, like the overlapping of shingles 
on a roof. This gives rise to a lined surface, 
much like the diffraction grating of the physi- 
cist, which is made by ruling a glass plate with 
thousands of parallel lines to the inch. Such a 
grating produces wonderful spectra, in which 
the rainbow colors are widely separated and 
very vivid. The principal on which this sep- 
aration of light depends is known as diffraction 
and cannot be explained here, but a similar 
effect takes place when light falls on the natur- 
ally ruled surface of a pearl and helps produce 
the play of colors known as iridescence. The 
thin layers themselves also help to produce the 
iridescence by interference of light much as in 



Pearls 263 

the case of the opal, which has already been 
discussed. 

Color. Having explained the cause of the 
orient and water of pearls, the color must next 
be considered. Pearls may be had of almost 
any color, but the majority of fine pearls are 
wilite, or nearly so. The fine Oriental pearls 
frequently have a creamy tint. Among fresh 
water pearls the creamy tint is less often seen, 
but fine pink tints occur. Occasionally a black 
pearl is found and on account of its rarity com- 
mands a price nearly as great as that obtainable 
for a white pearl of similar size and quality. 

The value of pearls depends upon several 
different factors and it is far from an easy matter 
to estimate the value of a fine specimen. It is 
much easier to grade and estimate the value of 
diamonds than to do the same for pearls, and it 
is only by long and intimate acquaintance with, 
the pearls themselves that one can hope to 
become expert in deciding values. There are, 
however, several general factors that govern 



264 Precious Stones 

the value of pearls. Chief among these are: 
I, Orient; 2, Color; 3, Texture or Skin; 4, Shape 
and Size. 

Factors Governing the Value of Pearls. Tak- 
ing up each of these factors in turn, it may be 
said of the first that unless a pearl has that fine 
keen luster known as a fine orient, it is of but 
limited value. No matter what the size, or 
how perfect the shape, it is nothing, if dead and 
lusterless. To have great value the gem must 
gleam with that soft but lively luster peculiar to 
fine specimens of pearl. With variations in 
orient go wide variations in value. 

As to color, the choicest pearls are pure white 
or delicate rose pink or creamy white. Pearls 
in these shades can be had in numbers and these 
colors are what might be called regular colors. 
Fancy colored pearls have peculiar and irregu- 
lar values, depending a good deal upon rarity 
and upon the obtaining of a customer for an 
odd color. Fine pink and fine black pearls are 
examples of the type that is meant here. 



Pearls 265 

To be very valuable a pearl must have 
a smooth even skin, that is, the texture of 
its surf ace must be even and regular. It must 
not have pits or scratches or wrinkles, or little 
raised spots upon it, or any cracks in it. In 
connection with this topic of "skin," it maybe 
meq^ioned that it is sometimes true that a pearl 
of bad skin or of poor luster may be improved 
markedly by "peeling" it, as the process is 
called. As was said above, a pearl is built in 
layers much like an onion, and it can often be 
peeled, that is, one or more layers can be 
removed, thus exposing fresh layers beneath, 
whose texture and luster may be better than 
those of the original outside layer. 

" Peeling " a Pearl. Possibly an anecdote 
of an actual case may serve best to explain the 
method by which "peeling" is sometimes 
accomplished. The writer was once at Vincen- 
nes, Ind., on business, and there became 
acquainted with a pearl buyer who was stopping 
at that place to buy fresh water pearls and 



266 Precious Stones 

"slugs" from the rivermen who gather the 
mussels for the sake of their shells. The 
latter are made into "pearl" buttons for 
clothing. It happened that the pearl buyer 
had accumulated some twenty-eight ounces of 
slugs and a number of pearls and was leaving 
on the same train with the author, who shared 
his seat with him. While we were looking 
over the slugs together the pearl buyer put his 
hand in his pocket and drew out a five dollar 
bill which he unrolled, exposing a pearl of about 
six grains, well shaped, but of rather dead 
luster. Remarking that he had paid but $4 for 
it and that he had rolled it up in the bill for safe 
keeping until he got time to peel it, he took out 
a small penknife, opened one of the blades, 
put a couple of kid glove finger tips on the 
thumb and first finger of his left hand and 
proceeded to peel the pearl on the moving 
train. Holding his two hands together to steady 
them, he pressed the edge of his knife blade 
against the pearl until the harder steel had 



Pearls 267 

penetrated straight down through one layer. 
Then with a flaking, lateral motion he flaked off 
a part of the outer skin. Bit by bit all of the 
outer layer was flaked off, and that, too, with- 
out appreciably scratching the next layer, so 
great was the worker's skill. When the pearl 
was completely peeled it was gently rubbed with 
three grades of polishing paper, each finer than 
the previous one, and then the writer was 
allowed to examine it. The appearance had 
been much improved, although it was not of 
extremely fine quality even when peeled. Under 
a high power magnifier scarcely a trace of the 
peeling could be seen. The value of the $4 pearl 
had been raised to at least $100 and not many 
minutes had been required for the change. 
A slower and more laborious, but safer, process 
of "peeling" a pearl, consists in gently rubbing 
the surface with a very fine, rather soft, abrasive 
powder until all of the outer skin has been thus 
worn away. 

Of course, in many such cases no better 



268 Precious Stones 

skin than the outer one could be found and 
disappointment would result from the peeling 
of such a pearl. It should be added that it will 
not do to try to peel a part of a pearl in order 
to remove an excrescence, for then one would 
inevitably cut across the layers, exposing their 
edges, and such a surface looks, when polished, 
much like a pearl button, but not like a pearl. 

In this connection may be mentioned the 
widespread belief on the part of the public 
that the concretions found in the common edible 
oyster can be polished by a lapidary, as a rough 
precious stone can be improved by the latter, and 
that a fine pearl will result. It is frequently 
necessary for jewelers to whom such "pearls" 
are brought, to undeceive the person bringing 
them and to tell him that only those molluscs 
that have a beautiful pearly lining to their 
shells are capable of producing true pearls and 
that the latter require no assistance from 
the lapidary. 

Shape. To return to the topic of factors gov- 



Pearls 269 

erning the value of pearls, the shape of the 
pearl makes a vast difference in the value. 
Perfectly spherical pearls are most highly 
valued and closely following come those of 
drop or pear shape, as this shape lends itself 
nicely to the making of pendants. Oval or egg 
shaped pearls are also good. After these come 
the button shapes, in which one side is flattened. 
Pearls of irregular shape are much less highly 
valued. The irregular shaped pearls are called 
baroque pearls in the trade. The rivermen 
engaged in the fresh water pearl fishery call 
them slugs. Some of the more regular of 
these are called "nuggets. " Others are termed 
"spikes" because of their pointed shape, and 
still others are called "wing" pearls on account 
of their resemblance to a bird's wing. Most of 
the baroques are too irregular in shape to have 
any special name applying to their form. 

Weight. After orient, color, skin, and shape 
have been considered, size or weight finally de- 
termines the value. Pearls are sold by an 



270 Precious Stones 

arbitrary unit of weight known as the pearl 
grain. It is not equal to the grain avoirdupois, 
but is one fourth of a diamond carat. As the 
new metric carat is one fifth of a gram and as 
there are 15.43 avoirdupois grains in a gram, it 
is seen at once that there are but 3.08 real 
grains in a carat rather than four. Thus 
the pearl grain is slightly lighter than the 
avoirdupois grain. 

Since large, fine pearls are exceedingly 
rare, the value mounts with size much more 
rapidly than is the case with any other gem; 
in fact, the value increases as the square of the 
weight. For example, let us consider two pearls, 
one of one grain weight, the other of two grains, 
and both of the same grade as to quality. If the 
smaller is worth say $2 per grain, then the 
larger is worth 2X2 (the square of the weight) 
times $2 (the price per grain base, as it is called 
in the trade), which totals $8. A four-grain 
pearl of this grade would be worth 4 X 4 X $2 
= $32, etc. Thus it is seen that the price 



Pearls 271 

increases very rapidly with increase in weight. 

Price " Per Grain Base." Some of the lower 
grades of pearls in small sizes are sold by the 
grain, straight, that is, the price per grain is 
merely multiplied by the weight in grains to get 
the value, just as the price per carat would 
be multiplied by the number of carats to get the 
value of a diamond. This method of figuring 
the value of pearls is used only for the cheaper 
grades and small sizes, however, and the method 
first explained, the calculation per grain base, 
is the one in universal use for fine gems. Very 
fine exceptional gems may be sold at a 
large price for the piece, regardless of the 
weight. 

It is interesting to note in this connection 
that Tavernier, the French gem merchant of the 
seventeenth century, tells us that in his day 
the price of large diamonds was calculated by 
a method similar to that which we now use 
for pearls, that is, the weight in carats was 
squared and the product multiplied by the price 



272 Precious Stones 

per carat. Such a method would give far too 
high a price for diamonds to-day. 

The High Price of Fine Pearls. This suggests 
the thought that pearls of fine quality and great 
size are the most costly of all gems to-day and 
yet there seems to be no halting in the demand 
for them. In fact, America is only just begin- 
ning to get interested in pearls and is com- 
ing to esteem them as they have long been 
esteemed in the East and in Europe, Those 
who have thought that the advance in the 
prices of diamonds in recent years will soon put 
them at prohibitive rates should consider the 
enormous prices that have been obtained and 
are being obtained for fine pearls. 

In order to facilitate the calculating of prices 
of pearls, tables have been computed and pub- 
lished giving the values of pearls of all sizes at 
different prices per grain base, and several times 
these tables have been outgrown, and new ones, 
running to higher values, have been made. 
The present tables run to $50 per grain base. 



Pearls 273 

There is much justification for the high 

prices demanded and paid for large and fine 

pearls. Such gems are really exceedingly scarce. 

Those who, as boys, have opened hundreds of 

river mussels only to find a very few small, 

badly misshapen "slugs" will realize that it is 

only one mollusc in a very large number that 

contains a fine pearl. Moreover, like the bison 

and the wild pigeon, the pearl-bearing molluscs 

may be greatly diminished in numbers or even 

exterminated by the greed of man and his 

fearfully destructive methods of harvesting 

nature's productions. In fact, the fisheries 

have been dwindling in yield for some time, 

and most of the fine pearls that are marketed 

are old pearls, already drilled, from the treasuries 

of Eastern potentates, who have been forced by 

necessity to accept the high prices offered by the 

West for part of their treasures. In India, pearls 

have long been acceptable collateral for loans, 

and many fine gems have come on the market 

after failure of the owners to repay such loans. 
18 



274 Precious Stones 

Having considered the factors bearing on the 
value of pearls, we will next consider briefly 
their physical properties. The specific gravity 
is less definite than with minerals and varies 
between 2.65 and 2.70. It may be even higher 
for pink pearls. 

Physical Properties. In hardness pearls also 
vary, ranging between 3^^ and 4 on Mohs' 
scale. They are thus very soft and easily worn 
or scratched by hard usage. A case showing 
the rather rapid wearing away of pearls recently 
came to the attention of the writer. A pendant 
in the shape of a Latin cross had been made 
of round pearls which had been drilled and 
strung on two slender gold rods to form the 
cross. The pearls were free to rotate on the 
wires. After a period of some twenty or more 
years of wear the pearls had all become distinctly 
cylindrical in shape, the rubbing against the 
garments over which the pendant had been 
worn having been sufficient to grind away 
the soft material to that extent. The luster 



Pearls 275 

was still good, the pearls having virtually 
been "peeled" very slowly by abrasion. 

Care of Pearls. This example suggests the 
great care that should be taken by owners of 
fine pearls to prevent undue rubbing or wear 
of these valuable but not extremely durable 
geqjs. They should be carefully wiped after 
being worn to remove dust and then put away 
in a tightly closed case. 

Pearls should never be allowed to come in 
contact with any acid, not even weak acids 
like lemonade, or punch or vinegar, as, being 
largely calcium carbonate they are very easily 
acted upon by acids, and a mere touch with an 
acid might ruin the surface luster. Being partly 
organic in nature, pearls are not everlasting, 
but must eventually decay, as is shown by the 
powdery condition of very old pearls that have 
been found with mummies or in ancient ruins. 
The organic matter has yielded to bacterial 
attack and decayed, leaving only the powdery 
mineral matter behind. As heat and moisture 



276 Precious Stones 

are the conditions mOvSt conducive to the growth 
of bacteria, and hence to decay, it would follow 
that fine pearls should be kept in a dry cool 
place when not in use. 



LESSON XXVIII 

CULTURED PEARLS AND IMITATIONS OF PEARLS 

Cultured Pearls. Like all very valuable 
gems, pearls have stimulated the ingenuity of 
man to attempt to make imitations that would 
pass for genuine. Perhaps the most ingenious, 
as well as the most natural looking product, 
is the '^cultured pearl.'" This is really natural 
pearl on much of its exterior, but artificial 
within and at the back. In order to bring 
about this result the Japanese, who originated 
the present commercial product, but who 
probably borrowed the original idea from the 
Chinese, call to their assistance the pearl oyster 
itself. The oysters are gently opened, small 
hemispherical disks of mother-of-pearl are in- 
troduced between shell and mantle and the 

oyster replanted. The foreign material is 

277 



278 Precious Stones 

coated by the oyster with true pearly lay- 
ers as usual, and after several years a suffi- 
ciently thick accumulation of pearly layers 
is thus deposited on the nucleus so that the 
oyster may be gathered and opened and the 
cultured pearl removed by sawing it out from 
the shell to which it has become attached. To 
the base is then neatly cemented a piece of 
mother-of-pearl to complete a nearly spherical 
shape, and the portions of the surface that have 
not been covered with true pearl are then 
polished. The product, when set in a proper 
pearl mounting, is quite convincing and really 
beautiful. 

As the time during which the oyster is 
allowed to work upon the cultured pearl is 
doubtless far less than is required for the 
growth of a large natural pearl, the num- 
ber of layers of true pearly material is con- 
siderably smaller than the number of layers 
that take part in the multiple reflections 
explained in the previous lesson, and hence 



Cultured and Imitation Pearls 279 

the "orient" of the cultured pearl is never 
equal to that of a fine true pearl. It is fre- 
quently very good however, and for uses 
that do not demand exposure of the whole 
surface of the pearl, the cultured pearl sup- 
plies a substitute for genuine pearls of moder- 
ate quality and price. The back parts of the 
cultured pearl, being only polished mother-of- 
pearl, have the appearance of the ordinary pearl 
button, rather than that of true pearl. 

Imitations of Pearls. Aside from these half 
artificial cultured pearls, the out and out imi- 
tations of pearls that have been most success- 
fully sold are of two general types, first '^ Roman 
pearls,'^ and, second, '' Indestructible pearls y 
The Roman pearls are made hollow and after- 
ward wax filled, the Indestructible pearls have 
solid enamel bases. In both types the pearly 
appearance is obtained by lining the interior, 
or coating the exterior, with more or less numer- 
ous layers of what is known as " nacre' ^ or some 
times as "essence d'oriente.'" This is prepared 



'280 Precious Stones 

from the scales of a small fish found in the North 
Sea and in Russia. The scales are removed and 
treated with certain solutions which remove 
the silvery powder from the scales. The "nacre " 
is then prepared from this powder. The fine- 
ness of the pearly effect becomes greater as 
the preparation ages, so very fine imitations are 
usually made from old "nacre.^^ The effect is 
also better the larger the number of successive 
layers used. The artificial pearl thus resembles 
the true pearl in the physical causes for the 
beautiful effect. 

In some cases the Roman pearl has a true 
iridescence which is produced by "burning" 
colors into the hollow enamel bead. Some of 
the indestructible pearls are made over beads of 
opalescent glass, thus imparting a finer effect 
to the finished product. While the cheaper 
grades of indestructible pearls have but three or 
four layers of nacre, some of the fine ones have 
as many as thirty or more. The earlier in- 
destructible pearls were made with a coating 



Cultured and Imitation Pearls 281 

material which was easily affected by heat, or 
by water, or by perspiration, as a gelatine-like 
sizing was included in it. The more recent 
product has a mineral binder which is not thus 
affected, so that the "pearls" are really about as 
durable as natural ones, and will at least last a 
lifetime if used with proper care. 

Like fine natural pearls, the fine imita- 
tions should be wiped after use and care- 
fully put away. They should also be re- 
strung occasionally, as should real pearls both 
to prevent loss by the breaking of the string 
and because the string becomes soiled after a 
time, and this hurts the appearance of the jewel.- 

The "Roman" type of imitation will not 
stand much heat, as the wax core would melt 
and run out. 

Testing Imitations of Pearls. As the mak- 
ing of imitations of pearls is mainly hand- 
work and as many treatments are required for 
the best imitations, fairly high prices are 
demanded for these better products, and the 



282 Precious Stones 

appearance and permanency warrant such 
prices. The best imitation pearls are really 
very difficult of detection except by close 
examination. They will not, of course, stand 
inspection under a high magnification. 

Artificial pearls may also be detected by 
their incorrect specific gravity, by their in- 
correct degree of hardness, and in the case 
of the hollow pearls by making a tiny ink 
spot upon the surface of the "pearl" and 
looking at it through a lens. A reflection 
of the spot from the inside surface of the bead 
will appear beside the spot itself if the pearl 
is of the Roman type. 

The artificial pearls so far described are 
high class products. Some of the very cheap 
and poor imitations are merely solid, or hollow, 
glass or enamel beads which have been made 
slightly pearly, either by adding various mate- 
rials to the glass or enamel when it was made, 
or by crudely coating the beads without or 
within with wax containing cheap "nacre." 



LESSON, XXIX 

THE USE OF BALANCES, AND THE UNIT OF WEIGHT 
IN USE FOR PRECIOUS STONES 

A S precious stones are almost always sold 
by weight, and as the value at stake is 
frequently very great, it is almost as neces- 
sary for a gem merchant, as it is for the chemist, 
to have delicate balances and to keep them in 
good order and to use them skillfully. 

A general understanding of the unit of 
weight in use for precious stones and how 
it is related to other standard weights is also 
necessary to the gem dealer. We will therefore 
consider in this lesson the use and care of 
balances and the nature and relative value of 
the unit of weight for precious stones. 

Delicate Balances Needed. As it is neces- 
sary, on account of their great value, to weigh 
283 



284 Precious Stones 

some gems, such as diamonds, emeralds, rubies, 
etc., with accuracy to at least the one hundredth 
part of a carat (which is roughly in the neigh- 
borhood of 1/15,000 of an ounce avoirdu- 
pois), balances of very delicate and accurate 
construction are a necessary part of the equip- 
ment of every gem merchant. While portable 
balances of a fair degree of accuracy are to be 
had, the best and surest balances are substanti- 
ally constructed and housed in glass cases, much 
as are those of the analytic chemist, which 
must do even finer weighing. The case pro- 
tects the balance from dust and dirt and pre- 
vents the action of air currents during the 
weighing. The balance itself has very delicate 
knife edges, sometimes of agate, sometimes 
of hardened steel, and these knife edges rest, 
when in use, on a block of agate or steel, so that 
there is a minimum amount of friction. When 
not in use the balance beam and knife edges 
are lifted from the block and held firmly by a 
metal arm, or else, as is the case with some bal- 



Balances and Unit of Weight 285 

ances, the post supporting the block is lowered, 
leaving the beam and knife edges out of con- 
tact with it. The object of this separation is 
to prevent any rough contact between the knife 
edges and the block on which they rest. Advan- 
tage should always be taken of this device 
whgnever any fairly heavy load is put on or 
taken off of either pan, as the sudden tip- 
ping of the beam might chip the knife edges 
if not supported. When the load is nearly 
balanced there may be no harm in carefully 
adding or removing small weights while the knife 
edges are resting on the block, but even then it is 
safer to lower the beam and pans. It should 
be needless to state that as level and rigid a 
support should be had for one's balance as 
circumstances permit. 

Method of Use of Balances. Before using a 
balance one should see that the pans are clean, 
that the base of the balance is properly leveled 
(the better balances have a spirit level attached) 
and that the pans balance each other without 



286 Precious Stones 

load. When slightly out of balance the defect 
may be adjusted by unscrewing the little adjust- 
ing nut at the end of the beam that is too light, 
or by screwing in the nut at the opposite end. 
Having seen that the adjustment is perfect 
the pans should be lowered and the object to be 
weighed placed on the left-hand pan (because a 
right handed person will find it handier to 
handle his weights on the right-hand pan). 
One should next guess as nearly as possible the 
weight of the stone and place well back on the 
right-hand pan the weight that he thinks comes 
nearest to that of the stone. If the weight is 
too heavy the next lighter weight should re- 
place it. Smaller weights should be added 
until a perfect balance is had, the small weights 
being neatly arranged in the order of their size, 
in order to more rapidly count them when the 
stone is balanced. This is the case when the 
pointer swings approximately equal distances 
to the right and to the left and there is then no 
need to wait for it to come to rest in the center. 



Balances and Unit of Weight 287 

It is well to count the weights as they lie on 
the pan (which is easily done if they have been 
arranged in descending order of size as sug- 
gested above) then write down the total, and on 
removing the weights count aloud as they are 
replaced in the box and note if the total checks 
that which was written down. It may seem 
unnecessary to be so careful in this matter, but 
it is better to be over-careful than to make a 
mistake where every hundredth of a carat 
may mean from one to five or six dollars or more. 
No dealer can afford to have a stone that he has 
sold prove to be lighter than he has stated it to 
be. One should be at least within one one- 
hundredth of a carat of the correct weight. 

It should be unnecessary to add that ac- 
curate weights should never be handled with the 
fingers. Ivory tipped forceps are best for 
handling the weights. The forceps commonly 
used for handling diamonds will, in time, wear 
away the weights by scratching them so that 
they will weigh materially less. Unless the 



288 Precious Stones 

weights are of platinum or plated with gold, the 
perspiration of the hands would cause them to 
oxidize and gain in weight. It would be well 
to discard the smaller weights, which are most 
in use, every few years and obtain new and 
accurate ones. In case this is not done one 
should at least have the weights checked 
against others known to be of standard weight. 
Any chemist will have balances and weights 
far more accurate than the best in use for 
precious stones and will gladly check the weights 
of a gem dealer for a moderate fee. 

To check the accuracy of your balance, 
change the stone and weights to opposite pans, 
in which case they should still balance. 

One should never overload a balance, both 
because the balance might be injired and 
because the relative accuracy decreases as 
the load increases. If the weight of a parcel 
of stones heavier than the total of the weights 
provided with the balance is desired, the parcel 
should be divided and weighed in parts. 



Balances and Unit of Weight 289 

While many dealers neglect some of the pre- 
cautions above suggested and somehow get 
along, yet it is safer to use care and to have cor- 
rect technique in the handling of one's balances. 

Having indicated a few of the refinements of 
method in weighing we will next consider the 
unit of weight in use for precious stones and see 
how it is related to other units of weight and in 
what manner it is subdivided. 

The Unit of Weight for Precious Stones. 

The present unit for precious stones in the 

United States is the metric carat. Most 

of the more progressive countries have in 

recent years agreed upon the use of this unit. 

Its use in the United States became general 

July I, 19 13. It is by definition exactly one 

fifth of a gram (the unit of weight of the Metric 

System of weights and measures). Its relation 

to the grain is that there are 3.08+ grains in the 

metric carat. The carat in use in this country 

up to a few years ago was about 2j4% heavier 

than, the present metric carat. It was equal to 
19 



290 Precious Stones 

.2053 grams instead of .2000 grams {}{ gram). 
The carats of countries not using the metric car- 
at vary considerably, but yet approximate the 
metric carat somewhat nearly. 

Thus, that in use in Great Britain was 
.2053 g., in Amsterdam .2057 g., in Berlin 
.20544 g., in Lisbon .20575 g., and in Florence 
0.1972 g. The latter was the only one that 
was under the metric carat. The change 
to the metric carat was desirable, as it unified 
the practice of weighing, which not only varied 
in different countries, but even in the same 
country. Thus there was no very exact agree- 
ment among the makers of diamond weights 
in the United States prior to the adoption of 
the metric carat. One man's carat was a bit 
heavier or lighter than another's. With a 
definite and simple relationship to the standard 
gram there is now no excuse for any variation 
in weights. The Bureau of Standards at 
Washington affords manufacturers every faci- 
lity for standardizing their weights. 



Balances and Unit of Weight 291 

The Decimal System of Subdivision of the 
Carat. With the adoption of the metric carat 
the custom of expressing parts of a carat 
in common fractions whose denominators 
were powers of the number 2 (^, X> 3^> ~ih, 
sV, "^4) was discarded as awkward and slow 
for. computation and the decimal system of 
subdivision was adopted. Thus the metric 
carat is divided into tenths and one hun- 
dredths. It is customary, however, to sum up 
the one hundredths and express them as the 
total number of one hundredths and not to ex- 
press them as tenths. Thus, a stone of 2.57 
carats is said to weigh "two and fifty-seven 
hundredths carats." The decimal system of 
subdivision of the carat makes the figuring of 
values simpler where no tables are handy. 
Of course, new tables were at once prepared 
when the new carat was adopted and they 
afford a rapid means of ascertaining the value 
of a storie of any weight when the price per carat 
is known. Should it become necessary to con- 



292 Precious Stones 

vert the weight of a stone from its expression in 
the old system to that of the new, one need only- 
get i.02}4% of the old weight. (The old carat 
was approximately .205 g., while the new one is 
.200 g. Hence one old carat 

.205 .I02>^ 

is = = i02>^% of a new one.) 

.200 .100 

Method of Converting Weights. If the old 

weight has fractions these should first be 
changed to decimals for convenience. For ex- 
ample, suppose it is wished to change 2]4 -h 
old carats to metric carats. X = -25 and -iV 
= .0625. Hence 2% 1-6=2.3125. Now get 
I02>^% of this: (2.3125 X 1.025 =2.37 metric 
carats). 

If, for any reason one should need to change 
from metric carats to old U. S. carats one should 
multiply by .9756 



(.200 g. \ 
= .9756 1 
.205 g. / 



>.205 g. 

As was said in Lesson XXV. pearls are sold 



Balances and Unit of Weight 293 

by the pearl grain, which is arbitrarily fixed at 
^ of a carat. With the change to the metric 
carat the pearl grain was correspondingly 
changed and its weight is now }i of .200 g. = 
.05 g., as expressed in the metric system. 



LESSON XXX 

TARIFF LAWS ON PRECIOUS AND IMITATION 
STONES 

OINCE it is necessary for a nation, as well as 
for an individual, to have an income, and 
since articles of luxury are more easily taxed 
than are those of necessity, the traffic in gems 
and their imitations has frequently been made a 
source of revenue to our government. Usually 
the per cent, charged as tariff has been com- 
paratively low, especially upon very valuable 
gems, such as diamonds and pearls, for the 
reason that too high a tariff would tend to tempt 
unscrupulous dealers to smuggle such goods 
into the country without declaring them. When 
the margin of difference between the values, 
with and without the tariff, is kept small the 

temptation is but slight, when the danger of 
294 



Tariff Laws 295 

detection and the drastic nature of the usual 
punishment are taken into account. Rough 
stones have frequently been allowed to enter 
the country duty free because they were re- 
garded as desirable raw materials which would 
afford employment to home industry. 

The tariff laws of October 3, 1913, made, 
however, some sweeping changes in the policy of 
our government toward precious stones and as 
those laws are still in force (April 4, 191 7) this 
lesson will attempt to set forth clearly the 
exact conditions under the present law. 

Perhaps the paragraph of first importance to 
the trade is No. 357 which reads as follows. 

" 357. Diamonds and other precious stones, 
rough or uncut, and not advanced in condi- 
tion or value from their natural state by cleav- 
ing, splitting, cutting, or other process, whether 
in their natural form or broken, and bort; 
any of the foregoing not set, and diamond dust, 
10 per centum ad valorem; pearls and parts 
thereof, drilled or undrilled, but not set or 



296 Precious Stones 

strung; diamonds, coral, rubies, cameos, and 
other precious stones and semi-precious stones, 
cut but not set, and suitable for use in the 
manufacture of jewelry, 20 per centum ad 
valorem; imitation precious stones, including 
pearls and parts thereof, for use in the manu- 
facture of jewelry, doublets, artificial, or so- 
called synthetic or reconstructed, pearls and 
parts thereof, rubies, or other precious stones, 
20 per centum ad valorem. " 

It will be noticed that the chief changes over 
the previous law are first that which imposes 
a 10% duty on rough precious stones, which 
were formerly free of duty, and second the 
advance in the duty on cut diamonds and other 
cut stones from the former 10% to the present 
20%. 

This increase in the tariff was regarded as 
unwise by many conservative importers, as 
the temptation to defraud the government is 
made much greater than before. The change 
was even feared by honest dealers who were 



Tariff Laws 297 

afraid that they could not successfully compete 
with dishonest importers who might smuggle 
gems into the country. In spite of a rather 
determined opposition the change was made 
and our most representative dealers have been 
making the best of the situation and have been 
doing all that they could to help prevent 
smuggling or at least reduce it to a minimum. 
Through their knowledge of the movements of 
diamond stocks and of prices they are able to 
detect any unduly large supply or any unwar- 
ranted lowness of price and thus to assist the 
government agents by directing investigation 
towards any dealer who seems to be enjoying 
immunity from the tariff. 

The question of the status of Japanese cul- 
tured pearls has been settled as follows. Para- 
graph 357 (quoted above) is ruled to cover 
them and they are thus subject to a 20% ad 
valorem tax. 

Carbonadoes — miners' diamonds — are free of 
duty, under paragraph 474. Crude minerals are 



298 Precious Stones 

also free of duty, paragraph 549. Paragraph 
607 declares "Specimens of natural history 
and mineralogy" are free. 

In case the owner is not prepared to pay the 
tax on imported mechandise the government 
holds the goods for a period of three years pend- 
ing such payments. 

In case an importer shows that imported 
merchandise was purchased at more than 
actual market value, he may deduct the differ- 
ence at time of entry and pay duty only on the 
wholesale foreign rnarket value, under Section 
III, paragraph i. 

On the other hand, if the examiner finds 
merchandise to be undervalued on the invoice, 
such merchandise is subject to additional penal 
duties, but in case of disagreement between 
the importer and the examiner as to the actual 
market value, appeal may be taken to the 
Customs Court. 

Since the Philippine Islands are possessions 
of the United States, pearls from those islands 



Tariff Laws 299 

may be admitted free of duty when the facts 
of their origin are certified to. 

In the case of precious stones which had their 
origin in the United States, but which were 
exported and kept for a time abroad it has been 
ruled that such stones may be imported into the 
United States free of duty. 

When precious or imitation precious stones 
are imported into the United States and sub- 
sequently mounted into jewelry which is then 
exported, the duty which was paid upon entry 
may be refunded less a deduction of i %. 

The author wishes to extend his thanks to 
Examiner W. B. Treadwell of New York, for his 
assistance in regard to the subject dealt with 
in this lesson. 



BIBLIOGRAPHY 

T^HE student of gems will, of course, want to read 
-^ many books on the subject and the following 
brief bibliography will enable the beginner to select 
his reading wisely from the start. Much more com- 
plete bibliographies will be found in some of the 
books listed here, one which is notably complete to 
date of publication is contained in Diamonds and 
Precious Stones, by Harry Emanual, F.R.G.S., 
London, John Camden Eatten, 1867. This covers 
many languages. 

The book which will probably be found most 
useful by those who have mastered this little text 
is the work by G. F, Herbert-Smith, to which fre- 
quent reference has been made at the close of many 
of our chapters. It is thoroughly scientific, yet 
understandable, and is very complete on the scien- 
tific side of the subject. 

301 



302 Bibliography 



Gem Stones, G. F. Herbert-Smith, Jas. Pott & 
Co., N. Y. 

For another work and one which contains in- 
formation of trade character as well as scientific 
information about gems see Precious Stones by 
W. R. Cattelle, J. B. Lippincott & Co., Phila., or see 
/ A Handbook of Precious Stones, by M. D. Roths- 
child, G. P. Putnam's Sons, N. Y. 

Gems and Gem Minerals, by Oliver Cummings 
Farrington, A. W. Mumford, publisher, Chicago, 
1903, is another good general work on gems. Its 
color plates of rough gem minerals are especially 
good. 

Those who are especially interested in the dia- 
mond should see The Diamond by W. R. Cattelle, 
The John Lane Co., N. Y., which gives a good ac- 
count of its subject and is rich in commercial in- 
formation, or Diamonds: A Study of the Factors 
which Govern their Value, by the present author, 
G. P. Putnam's Sons, N. Y., 1914. 

Sir Wm. Crook's, the Diamond, Harper & Bros., 
N. Y., is very interesting, especially in its account 
of the author's visits to the S. African mines, 



Bibliography 303 

Students of pearls will find The Book of the Pearl, 
by Dr. Geo. F. Kunz and Dr. Chas. Stevenson, 
Century Co., N. Y., very complete. A smaller \ 
work, yet a good one, on pearls is The Pearl by 
W. R. Cattelle, J. B. Lippincott & Co., Phila., 
1907. This book is strong on the commercialj 
side. 

rkn older work is Pearls and Pearling by D. Ed- 
win Streeter, Geo. Bell & Co., London. 

A work on gems and gem-cutting by a practical 
cutter is The Gem Cutter's Craft, by Leopold Clare- 
mont, Geo. Bell & Sons, London, but it should be 
said that very few trade secrets will be found ex- 
posed in the book. 

On the subject of scientific precious stones The 
Production and Identification 'of Artificial Precious 
Stones, by Noel Heaton, B.Sc, F.C.S., read before 
the Royal Society of Arts, Apr. 26, 191 1, is very 
fine. It may be had in the annual Report of the 
Smithsonian Institution for 191 1, p. 217. It gives 
one of the best accounts to be had of the history 
of the artificial production of precious stones, es- 
pecially of the corundum gems. It also contains 



X 



304 Bibliography 

a splendid account of how to distinguish scientific 
from natural gems. 

Most students of gems will need to refer fre- 
quently to some good text-book of mineralogy. 
Although old, Dana's Mineralogy is still a standard 
work. A newer book and one of a more popular 
nature is L, P. Gratacap's The Popular Guide to 
Minerals, D, Van Nostrand & Co., N. Y. 

Among larger and more expensive books on gems 
may be mentioned Precious Stones, by Dr. Max 
Bauer, This is an English translation of a German 
work which is a classic in its field. As it is now out 
of print in its English edition, a somewhat detailed 
account of its character may be of value to those 
who may be inclined to go to the effort to seek a 
copy at a public library or perhaps to purchase one 
through second-hand book stores. 

A popular account of their characters, occurrence 
and applications, with an introduction to their 
determination, for mineralogists, lapidaries, jewel- 
lers, etc. with an appendix on pearls and coral, by 
Dr. Max Bauer, Privy Councillor, professor in the 
Union of Marburg. Translated from the German 



Bibliography 3^5 

by L. J. Spencer, M.A. (Cantab.), F.G.S., assistant 
in the mineral department of the British Museum. 
With twenty plates and ninety-four figures in the 
text. London., Chas. Griffin & Co., Ltd.: Phila., 
J. B. Lippincott Co., 1904. 

The book is a large one. xv + 627 pages and is 
divided into three parts with an appendix on pearls 
andrcoral. 

Part L deals with the general characters of pre- 
cious stones. 

1 . Natural characters and occurrence. 

2. Applications of Precious Stones. 

3. Classification of Precious Stones. 106 pages. 
Part II. Systematic Description of Precious 

Stones, Diamond, Corundum Gems, Spinel, etc. 
450 pages. 

Part III. Determination and Distinguishing of 
Precious Stones. 20 pages. 

Appendix, 26 pages. Pearls and Coral. 

Bauer is exhaustive in his descriptions of the 
more important precious stones and he also de- 
scribes briefly very many little known and little 
used gem minerals. 



3o6 Bibliography 

On forms of cutting he is old fashioned. 

First 68 pages given to explanation of characters 
used in identifying stones. Good. 

On the Process of Cutting. Pages 79-87. Good 
account. More practical than most books give. 

Careful accounts of occurrence of precious stones 
with maps. 

Character of the occurrence of diamond in India, 
Brazil, and Africa, quite in detail. 

The student who wishes to master the subject 
of gems cannot afford to neglect Bauer. 

For those who read French, the latest, the most 
complete and thorough book on gems is Jean Es- 
card's Les Pierres Precieuses, H. Dunod et E.' Pinat, 
Paris, 1 9 14. 

It is a large and finely illustrated work,. 

The author has really outdone Bauer. The 
detail in regard to diamonds especially is very fine. 
Even the use of diamonds in mechanical ways is 
very completely gone into and also details in regard 
to cutting diamonds are very completely given. 
It is to be hoped that an English translation will 
soon become available. 



Bibliography 307 

Another large and thorough going work is 
Gardner F. WilHams' The Diamond Mines of South 
Africa, MacMillan, N. Y. 

Dr. Geo. F. Kunz's Gems and Precious Stones 
of North America, The Sci. Pub. Co., N. Y., 1890, 
336 pages,. 8 colored plates (excellent ones too), 
many engravings, is a very complete account of all 
published finds of precious stones in the United 
States, Canada, and Mexico, giving a popular de- 
scription of their value, history, archeology, and of 
the collections in which they exist, also a chapter 
on pearls and on remarkable foreign gems owned 
in the United States. Many rare and little known 
semi-precious stones are described here. Dr. Kunz 
is also the author of several more recent gem books 
notably The Magic of Jewels and Charms and The \ 
Curious Lore of Precious stones, Lippincott, Phila^__y 

Among books on engraved gems is the old Hand 
Book of Gem Engraving by C. W, King; Bell & 
Daldy, London, 1866, and one by Duifield Osborne; 
Henry Holt & Co., N. Y. Another book on this 
subject is Engraved Gems by Maxwell Somerville; 
Drexel Biddle, Phila. 



3o8 Bibliography 

For those who wish still further references the 
following older works will prove interesting. 

Precious Stones, by W. R. Cattelle; Lippincott, 
Phila. Precious Stones, by W. Goodchild; D. Van 
Nostrand & Co. N. Y. 

Julius Wodiska, of New York, has also written 
an interesting work on precious stones, A Book of 
Precious Stones, Putnams, 1907. 

Still older works are Precious Stones and Gems by 
Edwin W. Streetor; Chapman & Hall, London, 
1877. This is a book of 264 pages with nine illus- 
trations. It contains much of value and was un- 
surpassed in its day. Its first-hand accounts of 
nimierous important, even celebrated diamonds 
and other precious stones will always make it valu- 
able to the student of gems. 

Another book by the same author is The Great 
Diamonds of the World; Geo. Bell & Sons, London, 
1882; 321 pages. Not illustrated. Its title ade- 
quately describes its contents. It is an excellent 
work. The author even traveled in India tracing 
the history of some of the famous diamonds that 
he describes. 



Bibliography 309 

Diamonds and Precious Stones, by Louis Dieula- 
fait published in its English translation by Scribner, 
Armstrong & Co., N. Y., 1874, is another old but 
interesting work. It has 292 pages and 126 engrav- 
ings on wood. It gives a fine account of diamond 
cutting as practiced at that time. There is also 
an excellent history of the production of artificial 
precious stones to that date. 

The Natural History of Precious Stones and of 
the Precious Metals by C. W. King, M. A., Bell & 
Daldy, London, 1870, is rich in references to 
classical literature. 

One or two interesting monographs on precious 
stones have been written and The Tourmaline, by 
Augustus C. Hamlin is one of these. Mr. Hamlin 
became interested in gems because of his accidental 
discovery of some of the fine tourmalines of Maine. 
His Leisure Hours among the Gems is also very 
readable. Jas. R. Osgood & Co., Boston, 1884. It 
deals especially with diamond, emerald, opal, and 
sapphire. He gives a good account of American 
finds of diamond, and a long account of Euro- 
pean regalia. The book is full of interesting 



3IO Bibliography 

comment and contains many references to older 
authors. 

The Tears of the Heliades or Amber as a Gem, by 
W. Arnold Buffum, G. P. Putnam's Sons, N. Y., 
1900, is as its name implies a monograph on amber. 

A good work on the history of precious stones and 
on historical jewels is Gems and Jewels by Madame 
de Barrera; Richard Bentley, London, i860. It 
deals also with the geography of gem sources. 
An interesting chapter on "Great Jewel Robberies" 
is also included. 

Of still greater age but of great interest is John 
Mawe's old work on diamonds and precious stones. 
In it the author discusses in a conversational style 
that is very attractive much of the gem lore of his 
day and shows a profound knowledge of his subject, 
a knowledge that was evidently first hand and prac- 
tical, A Treatise on Diamonds and Precious Stones, 
by John Mawe, London. 2nd edition. Printed for 
and sold by the author. 

For readers of French, Jean Baptiste Tavernier's 
Voyages, in six volumes, will be vastly interesting. 
Ta vernier made six journeys to India and the East 



Bibliography 311 

between 1640 and 1680 as a gem merchant during 
which time he purchased and brought back to 
Europe many celebrated gems including the famous 
French blue diamond which he sold to Louis XIV 
and which was stolen at the robbery of the Garde 
Meuble during the French Revolution. Tavernier 
describes these famous stones and many others that 
hff was privileged to inspect in the treasuries of the 
Grand Mogul. He also describes interestingly and 
at great length the curious manners and customs 
of the people of the East. Les Six Voyages de 
Jean Baptiste Tavernier, etc., Nouvelle edition, 
Rouen, 1724. 

Pliny's Natural History, to go much further back, 
is full of references to gems, and gem students 
should run through it (it is to be had in English 
translation) for such interesting bits as that in 
which he describes the belief that quartz crystal 
results from the effect of very great cold upon ice, 
a belief which Pliny himself is careful not to sub- 
scribe to. He contents himself with relating what 
others believe in this regard. 

Both the Hebrew scriptures and the New Testa- 



312 Bibliography 

ment afford many references to gems with which the 
eager student of the subject should be familiar. 
"She is more precious than rubies" (referring to 
wisdom) is but one of these. 

In conclusion the author hopes that this little 
text may lead a few to pursue further this most 
fascinating theme and that the pursuit may bring 
much of pleasure as well as of profit. 



INDEX 















PAGE 


Absorption ....... 


. 15 


Adamantine luster . 






40, 41 


Agate .... 




128, 138, 


172, 197 


Alexandrite 




> • > 


. 140 


Almandite (see Garnet) 








Altered stones. 




247-249, 


250-257 


Amazonite 






. 176 


Amethyst 




94, 170, 


195, 196 


Aquamarine . 




. 


143, 189 


Azurite .... 




132, 148, 


177, 199 


Balances, Care and use of .... 


283-293 


Beryl .... 






84, 


143, 190 


Bibliography . 








. 301 


Bloodstone 












172 


Blue diamonds 












91 


Blue white diamonds 












91 


Brazilian diamonds . 












182 


Brilliancy 












203 


Brilliant cut stones . 












233 


Brilliant, Theory of the . 












205 


Brittleness of gems . 












119 


Brown stones . 












95 


Bubbles in gems 












103 


Bubbles in glass 












81 


Bubbles in scientific stones 












103 


Burmah rubies 












154 



313 



314 



Index 













PAGE 


Cabochons 






45, 216, 227 


Carbon . 










. 136 


Carborundum 










• 54.55,56 


Carnelian 










128, 138, 172 


Cat's-eye 










• 44-46, 138, 171 


Chalcedony 










. 138 


Chrysoberyl 






45 


85, 


122, 140, 157, 188 


Chrysoberyl cat's-eye 








45, 46, 85, 188 


Chrysolite 








. 176 


"Cinnamon stone " . 








• 144 


Citrine quartz 








161, 171, 195, 196 


Cleaving of diamonds 








.208 


Cleaving of precious stones 






.213 


Color, cause of, in minerals 






15 


Color of gems . 






.66-92 


Colorless stones 






• 97 


Corundum gems 


68-70, 


73, 


loi, 121, 134, 137 


Corundum gems, defects of 






. lOI 


Cultured pearls 






• 277-279 


Cutting of diamonds 






. 209 


Cutting of precious stones 






201-226 


Demantoid garnet . 


62, 64, 


82, 


130, 144, 169, 193 


Density of minerals . 






. 23 


Diamonds . . 6i, 73, 9 


[, 120, 


134, 


151-153, 179-186 


Dichroism 






. 15-22, 113 


Dichroscope, the 






17-20 


Dispersion 






60-65 


Double refraction 






5 


Doublets 






41, 241-246 


Emerald 




75 


-82, 143, 164, 189 


Emerald, wearing qualities of 






. 109 


Epidot .... 






9 


Extraordinary 


ray . 








. 16 



Index 



315 



Fancy diamonds 
"Fire," cause of 
Forms of precious stones 



PAGE 

. 207 
227-236 



vjrctiiiCL, .rLiiiictiiu.i i/C 

Garnet, Andradite . 


. 82, 130, 


ii(.^, luo, ly^ 
144, 169, 193 


Garnet, Demantoid . . 62, 


64, 82, 130, 


144, 169, 193 


Garnet, Pyrope . . . 


144, 


168, 192, 193 


Glass ..... 


. 


62, 142 


Glass imitations 


. 


81, 237-249 


"Golcondas" .... 


. 


. 180 


"Grain base," price of pearls per 


• 


. 271 


Hardness .... 


47-. 


54, 55-59, 113 


Hardness and wearing qualities 




I 19-132 


Hardness, Mohs's scale of 




48-51 


Hardness, table of . 




• 54 


Hardness, test of . . . 




• 51-54, 58 


"Heliodor" .... 




. 165 


"Hope Blue" diamond 




91 


Hyacinth .... 




. 166 


Imitations of precious stones 




• 237-249 


Imitations of pearls 




277-282 


Imperfections 




III 


Imperfections in corundum gems 




lOI 


Imperfections in glass 




81 


Imperfections in scientific stones 




. 104 


Jacinth ..... 




. 166 


Jade 


128, 


147, 175. 197 


Jadeite ..... 




128, 197 


Jargoons .... 




. 166 


Jasper . . . . . 




128, 172 



Kunzite 



195 



3i6 



Index 









PAGE 


Lapis lazuli .... 




132. 


177, 199 


Labradorite .... 






. 176 


Luster ..... 






38-42 


"Make" of diamonds 






205-207 


" Make " of precious stones 






. 220 


Malachite .... 


132, 


148, 


177, 199 


Metallic oxides 






• 137 


Mineral species 






133-148 


"Mixed cut" stones 






. 236 


Mohs's scale of hardness . 






48-51 


Moonstone . . . -4^ 


\, 45, I3i» 


146, 


176, 198 


Morganite . . . . . 






. 165 


"Nacre" .... 






. 280 


Naming precious stones . 


149 


-163, 


164-178 


Nephrite. .... 






129, 197 


Occurrence of precious stones . 






179-200 


"Olivine" {see demantoid garnet) 








Olivine ..... 






83, 176 


Onyx ..... 






. 172 


Opal 


44. 


131, 


139, 173 


Ordinary ray . 






16 


" Orient " of pearls . 






. 261 


"Oriental" stones 






84, 156 


"Paste" gems 




142 


237-241 


Pearls ..... 




. 


258-276 


"Peeling" pearls 






. 265 


Peridot 


. 8, 


130, 


176, 198 


Pink stones .... 




. 


• 93 


" Pinked " topaz 




. 


. 250 


Plasma ..... 




, 


. 172 


Polishing of diamonds 






. 210 


Polishing of precious stones 






. 218 


Prase ..... 






138, 172 



Index 



317 



Properties, definition of 
Purple stones . 

Quartz, . aventurine . 
Quartz, citrine. 
Quartz gems . 



PAGE 
I 

• 94 

. 171 
161, 171, 195, 196 

45, 127, 171, 195, 197 



Reflection, total 

Refraction 

Refraction, double 

Refraction, double, test for 

Refractometer, 

Rhodolite garnet 

"Roman" pearls 

Rose cut stones 

Rose quartz 

RubeUite 

Ruby 

Ruby, scientific 



. 204 

4 
. 8-13 
10, 112 

5 
. 168 

• 279 

• 231 

171, 197 

■ 93 
12, 67, 69, 153, 154, 186 

99-108 



Sapphires 

Sard 

Sardonyx 

Scientific stones 

Scientific stones, defects in 

Scientific stones, tests for 

Siam rubies 

Silicates 

"Silk" in rubies 

Slitting of precious stones 

South African diamonds 

Specific gravity 

Sphene 

Spinels . 

Spodumene 

Star stones 



63, 87, 88, 155, 187 
. 172 
. 172 
99-108 
. 104 
99-108 

• 154 
. 141 

• "7 
. 213 

. 184 

23-37. 114 
9, 62, 64 
71, 90, 123, 140, 158, 188 
95, 170, 195 
44. 46, 157 



3i8 



Index 









PAGE 


"Step cut" stones . 






. 235 


Structure of pearls . 






. 258 


Table, of hardness . 






. 54 


Table of refraction . 






12-13 


Table of specific gravity . 






• 29 


Tariff laws 






294-299 


Test for double refraction 






10 


Testing hardness 






51-54, 58 


Testing imitations of pearls 






. 281 


Testing unknown gems 






109-118 


Tiger's-eye 




45, 


138, 171 


Topaz .... 


67, 73. 91, 124, 


145, 


159, 189 


Toughness in stones 






• 119 


Tourmaline 


72, 77, 79-81, 96, 


146, 


167, 194 


"Triplets" 






79. 246 


Turquoise . . 




130, 


148, 198 


Unit of weight. 






. 289 


Varicite .... 




. 


. 148 


Vitreous luster 




, 


• 41 



Wearing qualities of gems . . . . .119 

Zircon ... 9, 62, 72, 92, 97, 125, 147, 166, 191 



\ 



